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 $245.44   9.209%   $268.0426   $268.04   $268.05   $268.00  
  Purchase #2 $174.96   11.382%   $194.8739   $194.87   $194.85   $194.90  
  Purchase #3 $215.49   11.363%   $239.9761   $239.98   $240.00   $240.00  
  Purchase #4 $94.67   3.429%   $97.9162   $97.92   $97.90   $97.90  
  Purchase #5 $147.38   10.274%   $162.5218   $162.52   $162.50   $162.50  
  Purchase #6 $188.51   6.679%   $201.1006   $201.10   $201.10   $201.10  
  Purchase #7 $177.87   10.455%   $196.4663   $196.47   $196.45   $196.50  
  7 purchase totals = $1,244.32       $1,360.8975   $1,360.90   $1,360.85   $1,360.90