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 $72.75   3.358%   $75.1929   $75.19   $75.20   $75.20  
  Purchase #2 $54.25   8.526%   $58.8754   $58.88   $58.90   $58.90  
  Purchase #3 $250.35   5.170%   $263.2931   $263.29   $263.30   $263.30  
  Purchase #4 $68.46   8.438%   $74.2367   $74.24   $74.25   $74.20  
  Purchase #5 $66.83   4.510%   $69.844   $69.84   $69.85   $69.80  
  Purchase #6 $191.32   13.708%   $217.5461   $217.55   $217.55   $217.50  
  Purchase #7 $226.42   7.679%   $243.8068   $243.81   $243.80   $243.80  
  7 purchase totals = $930.38       $1,002.7950   $1,002.80   $1,002.85   $1,002.70