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 $205.91   8.760%   $223.9477   $223.95   $223.95   $223.90  
  Purchase #2 $217.41   12.371%   $244.3058   $244.31   $244.30   $244.30  
  Purchase #3 $82.77   5.549%   $87.3629   $87.36   $87.35   $87.40  
  Purchase #4 $249.32   7.637%   $268.3606   $268.36   $268.35   $268.40  
  Purchase #5 $84.43   5.738%   $89.2746   $89.27   $89.25   $89.30  
  Purchase #6 $168.58   5.836%   $178.4183   $178.42   $178.40   $178.40  
  Purchase #7 $159.82   11.270%   $177.8317   $177.83   $177.85   $177.80  
  7 purchase totals = $1,168.24       $1,269.5016   $1,269.50   $1,269.45   $1,269.50