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 $250.32   8.291%   $271.074   $271.07   $271.05   $271.10  
  Purchase #2 $54.57   8.106%   $58.9934   $58.99   $59.00   $59.00  
  Purchase #3 $151.34   9.142%   $165.1755   $165.18   $165.20   $165.20  
  Purchase #4 $26.81   6.800%   $28.6331   $28.63   $28.65   $28.60  
  Purchase #5 $91.58   6.722%   $97.736   $97.74   $97.75   $97.70  
  Purchase #6 $163.51   9.423%   $178.9175   $178.92   $178.90   $178.90  
  Purchase #7 $58.46   7.261%   $62.7048   $62.70   $62.70   $62.70  
  7 purchase totals = $796.59       $863.2343   $863.23   $863.25   $863.20