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 $68.96   5.782%   $72.9473   $72.95   $72.95   $72.90  
  Purchase #2 $36.53   6.718%   $38.9841   $38.98   $39.00   $39.00  
  Purchase #3 $60.92   10.562%   $67.3544   $67.35   $67.35   $67.40  
  Purchase #4 $221.67   4.624%   $231.92   $231.92   $231.90   $231.90  
  Purchase #5 $64.67   6.195%   $68.6763   $68.68   $68.70   $68.70  
  Purchase #6 $28.66   11.478%   $31.9496   $31.95   $31.95   $31.90  
  Purchase #7 $235.61   6.827%   $251.6951   $251.70   $251.70   $251.70  
  7 purchase totals = $717.02       $763.5268   $763.53   $763.55   $763.50