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 $241.52   6.604%   $257.47   $257.47   $257.45   $257.50  
  Purchase #2 $158.99   11.712%   $177.6109   $177.61   $177.60   $177.60  
  Purchase #3 $176.31   5.601%   $186.1851   $186.19   $186.20   $186.20  
  Purchase #4 $168.91   5.864%   $178.8149   $178.81   $178.80   $178.80  
  Purchase #5 $87.29   5.375%   $91.9818   $91.98   $92.00   $92.00  
  Purchase #6 $28.38   4.873%   $29.763   $29.76   $29.75   $29.80  
  Purchase #7 $23.26   3.697%   $24.1199   $24.12   $24.10   $24.10  
  7 purchase totals = $884.66       $945.9456   $945.94   $945.90   $946.00