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 $238.89   10.484%   $263.9352   $263.94   $263.95   $263.90  
  Purchase #2 $232.33   9.251%   $253.8228   $253.82   $253.80   $253.80  
  Purchase #3 $126.37   7.225%   $135.5002   $135.50   $135.50   $135.50  
  Purchase #4 $104.75   7.815%   $112.9362   $112.94   $112.95   $112.90  
  Purchase #5 $250.33   10.650%   $276.9901   $276.99   $277.00   $277.00  
  Purchase #6 $154.52   13.652%   $175.6151   $175.62   $175.60   $175.60  
  Purchase #7 $33.57   8.560%   $36.4436   $36.44   $36.45   $36.40  
  7 purchase totals = $1,140.76       $1,255.2432   $1,255.25   $1,255.25   $1,255.10