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 $67.91   11.580%   $75.774   $75.77   $75.75   $75.80  
  Purchase #2 $209.39   11.625%   $233.7316   $233.73   $233.75   $233.70  
  Purchase #3 $64.97   8.661%   $70.5971   $70.60   $70.60   $70.60  
  Purchase #4 $85.68   4.597%   $89.6187   $89.62   $89.60   $89.60  
  Purchase #5 $161.32   8.136%   $174.445   $174.45   $174.45   $174.40  
  Purchase #6 $168.30   5.756%   $177.9873   $177.99   $178.00   $178.00  
  Purchase #7 $136.48   3.318%   $141.0084   $141.01   $141.00   $141.00  
  7 purchase totals = $894.05       $963.1621   $963.17   $963.15   $963.10