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 $185.43   11.774%   $207.2625   $207.26   $207.25   $207.30  
  Purchase #2 $234.64   4.260%   $244.6357   $244.64   $244.65   $244.60  
  Purchase #3 $38.93   9.645%   $42.6848   $42.68   $42.70   $42.70  
  Purchase #4 $59.32   7.818%   $63.9576   $63.96   $63.95   $64.00  
  Purchase #5 $235.32   5.627%   $248.5615   $248.56   $248.55   $248.60  
  Purchase #6 $107.43   11.322%   $119.5932   $119.59   $119.60   $119.60  
  Purchase #7 $155.73   10.584%   $172.2125   $172.21   $172.20   $172.20  
  7 purchase totals = $1,016.80       $1,098.9078   $1,098.90   $1,098.90   $1,099.00