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 $119.93   3.843%   $124.5389   $124.54   $124.55   $124.50  
  Purchase #2 $153.51   10.605%   $169.7897   $169.79   $169.80   $169.80  
  Purchase #3 $245.42   5.224%   $258.2407   $258.24   $258.25   $258.20  
  Purchase #4 $238.36   11.295%   $265.2828   $265.28   $265.30   $265.30  
  Purchase #5 $49.55   6.795%   $52.9169   $52.92   $52.90   $52.90  
  Purchase #6 $217.45   8.143%   $235.157   $235.16   $235.15   $235.20  
  Purchase #7 $192.36   5.252%   $202.4627   $202.46   $202.45   $202.50  
  7 purchase totals = $1,216.58       $1,308.3887   $1,308.39   $1,308.40   $1,308.40