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 $154.94   13.455%   $175.7872   $175.79   $175.80   $175.80  
  Purchase #2 $189.78   6.195%   $201.5369   $201.54   $201.55   $201.50  
  Purchase #3 $9.84   8.306%   $10.6573   $10.66   $10.65   $10.70  
  Purchase #4 $41.89   8.805%   $45.5784   $45.58   $45.60   $45.60  
  Purchase #5 $219.38   7.825%   $236.5465   $236.55   $236.55   $236.50  
  Purchase #6 $97.78   6.664%   $104.2961   $104.30   $104.30   $104.30  
  Purchase #7 $248.55   9.586%   $272.376   $272.38   $272.40   $272.40  
  7 purchase totals = $962.16       $1,046.7784   $1,046.80   $1,046.85   $1,046.80