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 $206.74   8.860%   $225.0572   $225.06   $225.05   $225.10  
  Purchase #2 $206.78   12.518%   $232.6647   $232.66   $232.65   $232.70  
  Purchase #3 $106.95   7.198%   $114.6483   $114.65   $114.65   $114.60  
  Purchase #4 $54.58   11.684%   $60.9571   $60.96   $60.95   $61.00  
  Purchase #5 $53.43   10.307%   $58.937   $58.94   $58.95   $58.90  
  Purchase #6 $59.42   3.613%   $61.5668   $61.57   $61.55   $61.60  
  Purchase #7 $187.41   8.259%   $202.8882   $202.89   $202.90   $202.90  
  7 purchase totals = $875.31       $956.7193   $956.73   $956.70   $956.80