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 $216.87   8.283%   $234.8333   $234.83   $234.85   $234.80  
  Purchase #2 $28.33   3.557%   $29.3377   $29.34   $29.35   $29.30  
  Purchase #3 $38.76   4.657%   $40.5651   $40.57   $40.55   $40.60  
  Purchase #4 $95.42   6.644%   $101.7597   $101.76   $101.75   $101.80  
  Purchase #5 $24.93   8.445%   $27.0353   $27.04   $27.05   $27.00  
  Purchase #6 $207.76   13.199%   $235.1822   $235.18   $235.20   $235.20  
  Purchase #7 $231.49   10.732%   $256.3335   $256.33   $256.35   $256.30  
  7 purchase totals = $843.56       $925.0468   $925.05   $925.10   $925.00