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 $25.53   6.775%   $27.2597   $27.26   $27.25   $27.30  
  Purchase #2 $206.42   4.185%   $215.0587   $215.06   $215.05   $215.10  
  Purchase #3 $24.52   10.146%   $27.0078   $27.01   $27.00   $27.00  
  Purchase #4 $53.68   13.145%   $60.7362   $60.74   $60.75   $60.70  
  Purchase #5 $101.80   5.577%   $107.4774   $107.48   $107.50   $107.50  
  Purchase #6 $199.78   4.587%   $208.9439   $208.94   $208.95   $208.90  
  Purchase #7 $194.78   5.779%   $206.0363   $206.04   $206.05   $206.00  
  7 purchase totals = $806.51       $852.5200   $852.53   $852.55   $852.50