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 $169.43   10.679%   $187.5234   $187.52   $187.50   $187.50  
  Purchase #2 $200.58   6.423%   $213.4633   $213.46   $213.45   $213.50  
  Purchase #3 $236.25   12.858%   $266.627   $266.63   $266.65   $266.60  
  Purchase #4 $59.60   3.484%   $61.6765   $61.68   $61.70   $61.70  
  Purchase #5 $67.92   11.363%   $75.6377   $75.64   $75.65   $75.60  
  Purchase #6 $142.80   10.837%   $158.2752   $158.28   $158.30   $158.30  
  Purchase #7 $183.63   10.733%   $203.339   $203.34   $203.35   $203.30  
  7 purchase totals = $1,060.21       $1,166.5421   $1,166.55   $1,166.60   $1,166.50