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 $245.33   12.218%   $275.3044   $275.30   $275.30   $275.30  
  Purchase #2 $213.73   7.287%   $229.3045   $229.30   $229.30   $229.30  
  Purchase #3 $140.97   13.618%   $160.1673   $160.17   $160.15   $160.20  
  Purchase #4 $36.53   5.479%   $38.5315   $38.53   $38.55   $38.50  
  Purchase #5 $232.65   6.389%   $247.514   $247.51   $247.50   $247.50  
  Purchase #6 $228.95   3.535%   $237.0434   $237.04   $237.05   $237.00  
  Purchase #7 $243.63   9.269%   $266.2121   $266.21   $266.20   $266.20  
  7 purchase totals = $1,341.79       $1,454.0772   $1,454.06   $1,454.05   $1,454.00