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 $60.66   6.306%   $64.4852   $64.49   $64.50   $64.50  
  Purchase #2 $216.70   7.134%   $232.1594   $232.16   $232.15   $232.20  
  Purchase #3 $210.96   13.199%   $238.8046   $238.80   $238.80   $238.80  
  Purchase #4 $29.79   7.745%   $32.0972   $32.10   $32.10   $32.10  
  Purchase #5 $200.32   9.584%   $219.5187   $219.52   $219.50   $219.50  
  Purchase #6 $205.63   9.130%   $224.404   $224.40   $224.40   $224.40  
  Purchase #7 $234.82   6.347%   $249.724   $249.72   $249.70   $249.70  
  7 purchase totals = $1,158.88       $1,261.1931   $1,261.19   $1,261.15   $1,261.20