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 $56.94   4.790%   $59.6674   $59.67   $59.65   $59.70  
  Purchase #2 $249.54   8.356%   $270.3916   $270.39   $270.40   $270.40  
  Purchase #3 $217.47   8.824%   $236.6596   $236.66   $236.65   $236.70  
  Purchase #4 $186.57   13.603%   $211.9491   $211.95   $211.95   $211.90  
  Purchase #5 $64.57   13.746%   $73.4458   $73.45   $73.45   $73.40  
  Purchase #6 $250.65   11.536%   $279.565   $279.57   $279.55   $279.60  
  Purchase #7 $158.61   10.263%   $174.8881   $174.89   $174.90   $174.90  
  7 purchase totals = $1,184.35       $1,306.5666   $1,306.58   $1,306.55   $1,306.60