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 $32.62   12.616%   $36.7353   $36.74   $36.75   $36.70  
  Purchase #2 $27.45   4.503%   $28.6861   $28.69   $28.70   $28.70  
  Purchase #3 $128.95   6.113%   $136.8327   $136.83   $136.85   $136.80  
  Purchase #4 $151.89   3.370%   $157.0087   $157.01   $157.00   $157.00  
  Purchase #5 $227.98   11.740%   $254.7449   $254.74   $254.75   $254.70  
  Purchase #6 $80.57   10.303%   $88.8711   $88.87   $88.85   $88.90  
  Purchase #7 $244.81   5.725%   $258.8254   $258.83   $258.85   $258.80  
  7 purchase totals = $894.27       $961.7042   $961.71   $961.75   $961.60