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 $113.46   10.141%   $124.966   $124.97   $124.95   $125.00  
  Purchase #2 $10.41   3.464%   $10.7706   $10.77   $10.75   $10.80  
  Purchase #3 $213.41   6.773%   $227.8643   $227.86   $227.85   $227.90  
  Purchase #4 $55.85   11.579%   $62.3169   $62.32   $62.30   $62.30  
  Purchase #5 $9.71   13.524%   $11.0232   $11.02   $11.00   $11.00  
  Purchase #6 $202.46   8.788%   $220.2522   $220.25   $220.25   $220.30  
  Purchase #7 $225.34   11.634%   $251.5561   $251.56   $251.55   $251.60  
  7 purchase totals = $830.64       $908.7493   $908.75   $908.65   $908.90