Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.93   11.788%   $268.2129   $268.21   $268.20   $268.20  
  Purchase #2 $138.36   12.497%   $155.6508   $155.65   $155.65   $155.70  
  Purchase #3 $143.77   3.124%   $148.2614   $148.26   $148.25   $148.30  
  Purchase #4 $96.56   11.731%   $107.8875   $107.89   $107.90   $107.90  
  Purchase #5 $212.58   13.367%   $240.9956   $241.00   $241.00   $241.00  
  Purchase #6 $218.69   11.847%   $244.5982   $244.60   $244.60   $244.60  
  Purchase #7 $176.69   4.316%   $184.3159   $184.32   $184.30   $184.30  
  7 purchase totals = $1,226.58       $1,349.9223   $1,349.93   $1,349.90   $1,350.00