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 $54.26   10.766%   $60.1016   $60.10   $60.10   $60.10  
  Purchase #2 $13.32   8.208%   $14.4133   $14.41   $14.40   $14.40  
  Purchase #3 $244.92   7.706%   $263.7935   $263.79   $263.80   $263.80  
  Purchase #4 $62.48   7.697%   $67.2891   $67.29   $67.30   $67.30  
  Purchase #5 $127.92   8.371%   $138.6282   $138.63   $138.65   $138.60  
  Purchase #6 $203.37   7.551%   $218.7265   $218.73   $218.75   $218.70  
  Purchase #7 $76.59   11.486%   $85.3871   $85.39   $85.40   $85.40  
  7 purchase totals = $782.86       $848.3393   $848.34   $848.40   $848.30