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 $241.79   9.680%   $265.1953   $265.20   $265.20   $265.20  
  Purchase #2 $89.62   5.651%   $94.6844   $94.68   $94.70   $94.70  
  Purchase #3 $101.29   9.321%   $110.7312   $110.73   $110.75   $110.70  
  Purchase #4 $48.27   7.121%   $51.7073   $51.71   $51.70   $51.70  
  Purchase #5 $182.36   6.225%   $193.7119   $193.71   $193.70   $193.70  
  Purchase #6 $91.93   7.298%   $98.6391   $98.64   $98.65   $98.60  
  Purchase #7 $221.28   6.421%   $235.4884   $235.49   $235.50   $235.50  
  7 purchase totals = $976.54       $1,050.1576   $1,050.16   $1,050.20   $1,050.10