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 $234.97   11.490%   $261.9681   $261.97   $261.95   $262.00  
  Purchase #2 $243.98   9.715%   $267.6827   $267.68   $267.70   $267.70  
  Purchase #3 $104.51   5.713%   $110.4807   $110.48   $110.50   $110.50  
  Purchase #4 $58.46   8.695%   $63.5431   $63.54   $63.55   $63.50  
  Purchase #5 $200.44   6.336%   $213.1399   $213.14   $213.15   $213.10  
  Purchase #6 $96.95   9.678%   $106.3328   $106.33   $106.35   $106.30  
  Purchase #7 $216.84   9.407%   $237.2381   $237.24   $237.25   $237.20  
  7 purchase totals = $1,156.15       $1,260.3854   $1,260.38   $1,260.45   $1,260.30