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 $60.70   5.667%   $64.1399   $64.14   $64.15   $64.10  
  Purchase #2 $189.25   6.668%   $201.8692   $201.87   $201.85   $201.90  
  Purchase #3 $32.80   12.614%   $36.9374   $36.94   $36.95   $36.90  
  Purchase #4 $214.75   10.778%   $237.8958   $237.90   $237.90   $237.90  
  Purchase #5 $53.36   9.740%   $58.5573   $58.56   $58.55   $58.60  
  Purchase #6 $5.39   12.541%   $6.066   $6.07   $6.05   $6.10  
  Purchase #7 $29.55   10.565%   $32.672   $32.67   $32.65   $32.70  
  7 purchase totals = $585.80       $638.1376   $638.15   $638.10   $638.20