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 $205.86   9.427%   $225.2664   $225.27   $225.25   $225.30  
  Purchase #2 $80.73   8.707%   $87.7592   $87.76   $87.75   $87.80  
  Purchase #3 $98.51   11.856%   $110.1893   $110.19   $110.20   $110.20  
  Purchase #4 $78.93   7.444%   $84.8055   $84.81   $84.80   $84.80  
  Purchase #5 $80.82   10.479%   $89.2891   $89.29   $89.30   $89.30  
  Purchase #6 $97.77   8.236%   $105.8223   $105.82   $105.80   $105.80  
  Purchase #7 $174.42   7.685%   $187.8242   $187.82   $187.80   $187.80  
  7 purchase totals = $817.04       $890.9560   $890.96   $890.90   $891.00