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 $55.79   13.849%   $63.5164   $63.52   $63.50   $63.50  
  Purchase #2 $83.84   12.481%   $94.3041   $94.30   $94.30   $94.30  
  Purchase #3 $96.72   7.571%   $104.0427   $104.04   $104.05   $104.00  
  Purchase #4 $146.74   6.486%   $156.2576   $156.26   $156.25   $156.30  
  Purchase #5 $201.42   4.103%   $209.6843   $209.68   $209.70   $209.70  
  Purchase #6 $89.53   5.355%   $94.3243   $94.32   $94.30   $94.30  
  Purchase #7 $28.91   11.539%   $32.2459   $32.25   $32.25   $32.20  
  7 purchase totals = $702.95       $754.3753   $754.37   $754.35   $754.30