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 $53.97   11.860%   $60.3708   $60.37   $60.35   $60.40  
  Purchase #2 $74.78   9.596%   $81.9559   $81.96   $81.95   $82.00  
  Purchase #3 $128.79   3.559%   $133.3736   $133.37   $133.35   $133.40  
  Purchase #4 $14.46   6.713%   $15.4307   $15.43   $15.45   $15.40  
  Purchase #5 $192.43   4.266%   $200.6391   $200.64   $200.65   $200.60  
  Purchase #6 $18.84   3.682%   $19.5337   $19.53   $19.55   $19.50  
  Purchase #7 $137.95   9.433%   $150.9628   $150.96   $150.95   $151.00  
  7 purchase totals = $621.22       $662.2666   $662.26   $662.25   $662.30