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 $192.58   4.377%   $201.0092   $201.01   $201.00   $201.00  
  Purchase #2 $112.37   11.225%   $124.9835   $124.98   $125.00   $125.00  
  Purchase #3 $149.62   5.468%   $157.8012   $157.80   $157.80   $157.80  
  Purchase #4 $100.39   5.643%   $106.055   $106.06   $106.05   $106.10  
  Purchase #5 $16.53   4.716%   $17.3096   $17.31   $17.30   $17.30  
  Purchase #6 $215.81   9.140%   $235.535   $235.54   $235.55   $235.50  
  Purchase #7 $73.73   12.720%   $83.1085   $83.11   $83.10   $83.10  
  7 purchase totals = $861.03       $925.8020   $925.81   $925.80   $925.80