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 $54.67   7.850%   $58.9616   $58.96   $58.95   $59.00  
  Purchase #2 $25.79   4.629%   $26.9838   $26.98   $27.00   $27.00  
  Purchase #3 $210.67   8.774%   $229.1542   $229.15   $229.15   $229.20  
  Purchase #4 $192.87   9.200%   $210.614   $210.61   $210.60   $210.60  
  Purchase #5 $164.89   4.279%   $171.9456   $171.95   $171.95   $171.90  
  Purchase #6 $87.44   9.119%   $95.4137   $95.41   $95.40   $95.40  
  Purchase #7 $127.33   7.471%   $136.8428   $136.84   $136.85   $136.80  
  7 purchase totals = $863.66       $929.9157   $929.90   $929.90   $929.90