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 $232.70   12.268%   $261.2476   $261.25   $261.25   $261.20  
  Purchase #2 $77.31   11.840%   $86.4635   $86.46   $86.45   $86.50  
  Purchase #3 $156.32   7.426%   $167.9283   $167.93   $167.95   $167.90  
  Purchase #4 $94.93   9.664%   $104.104   $104.10   $104.10   $104.10  
  Purchase #5 $245.78   7.504%   $264.2233   $264.22   $264.20   $264.20  
  Purchase #6 $117.70   5.836%   $124.569   $124.57   $124.55   $124.60  
  Purchase #7 $66.92   10.607%   $74.0182   $74.02   $74.00   $74.00  
  7 purchase totals = $991.66       $1,082.5539   $1,082.55   $1,082.50   $1,082.50