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 $186.77   7.398%   $200.5872   $200.59   $200.60   $200.60  
  Purchase #2 $54.42   3.352%   $56.2442   $56.24   $56.25   $56.20  
  Purchase #3 $226.42   13.834%   $257.7429   $257.74   $257.75   $257.70  
  Purchase #4 $63.64   4.168%   $66.2925   $66.29   $66.30   $66.30  
  Purchase #5 $226.65   11.782%   $253.3539   $253.35   $253.35   $253.40  
  Purchase #6 $187.81   3.453%   $194.2951   $194.30   $194.30   $194.30  
  Purchase #7 $45.95   4.705%   $48.1119   $48.11   $48.10   $48.10  
  7 purchase totals = $991.66       $1,076.6277   $1,076.62   $1,076.65   $1,076.60