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 $88.73   8.739%   $96.4841   $96.48   $96.50   $96.50  
  Purchase #2 $27.88   12.242%   $31.2931   $31.29   $31.30   $31.30  
  Purchase #3 $132.90   3.856%   $138.0246   $138.02   $138.00   $138.00  
  Purchase #4 $45.49   13.629%   $51.6898   $51.69   $51.70   $51.70  
  Purchase #5 $91.38   8.759%   $99.384   $99.38   $99.40   $99.40  
  Purchase #6 $14.45   6.754%   $15.426   $15.43   $15.45   $15.40  
  Purchase #7 $30.37   8.804%   $33.0438   $33.04   $33.05   $33.00  
  7 purchase totals = $431.20       $465.3454   $465.33   $465.40   $465.30