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 $226.47   7.340%   $243.0929   $243.09   $243.10   $243.10  
  Purchase #2 $48.29   11.173%   $53.6854   $53.69   $53.70   $53.70  
  Purchase #3 $82.73   12.584%   $93.1407   $93.14   $93.15   $93.10  
  Purchase #4 $121.99   4.333%   $127.2758   $127.28   $127.30   $127.30  
  Purchase #5 $43.87   10.684%   $48.5571   $48.56   $48.55   $48.60  
  Purchase #6 $152.95   13.383%   $173.4193   $173.42   $173.40   $173.40  
  Purchase #7 $245.38   10.672%   $271.567   $271.57   $271.55   $271.60  
  7 purchase totals = $921.68       $1,010.7382   $1,010.75   $1,010.75   $1,010.80