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 $47.76   13.591%   $54.2511   $54.25   $54.25   $54.30  
  Purchase #2 $234.71   8.502%   $254.665   $254.67   $254.65   $254.70  
  Purchase #3 $86.50   13.586%   $98.2519   $98.25   $98.25   $98.30  
  Purchase #4 $189.85   10.532%   $209.845   $209.85   $209.85   $209.80  
  Purchase #5 $32.86   10.519%   $36.3165   $36.32   $36.30   $36.30  
  Purchase #6 $205.35   11.313%   $228.5812   $228.58   $228.60   $228.60  
  Purchase #7 $77.88   9.392%   $85.1945   $85.19   $85.20   $85.20  
  7 purchase totals = $874.91       $967.1052   $967.11   $967.10   $967.20