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 $56.99   11.390%   $63.4812   $63.48   $63.50   $63.50  
  Purchase #2 $143.91   8.346%   $155.9207   $155.92   $155.90   $155.90  
  Purchase #3 $242.60   9.452%   $265.5306   $265.53   $265.55   $265.50  
  Purchase #4 $90.51   7.804%   $97.5734   $97.57   $97.55   $97.60  
  Purchase #5 $134.52   12.235%   $150.9785   $150.98   $151.00   $151.00  
  Purchase #6 $117.66   4.728%   $123.223   $123.22   $123.20   $123.20  
  Purchase #7 $27.37   4.677%   $28.6501   $28.65   $28.65   $28.70  
  7 purchase totals = $813.56       $885.3575   $885.35   $885.35   $885.40