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 $208.85   8.237%   $226.053   $226.05   $226.05   $226.10  
  Purchase #2 $235.47   8.351%   $255.1341   $255.13   $255.15   $255.10  
  Purchase #3 $94.79   3.465%   $98.0745   $98.07   $98.05   $98.10  
  Purchase #4 $174.46   9.485%   $191.0075   $191.01   $191.00   $191.00  
  Purchase #5 $183.50   9.548%   $201.0206   $201.02   $201.00   $201.00  
  Purchase #6 $229.67   4.832%   $240.7677   $240.77   $240.75   $240.80  
  Purchase #7 $149.89   12.199%   $168.1751   $168.18   $168.20   $168.20  
  7 purchase totals = $1,276.63       $1,380.2325   $1,380.23   $1,380.20   $1,380.30