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 $73.64   13.377%   $83.4908   $83.49   $83.50   $83.50  
  Purchase #2 $210.38   9.590%   $230.5554   $230.56   $230.55   $230.60  
  Purchase #3 $75.80   8.599%   $82.318   $82.32   $82.30   $82.30  
  Purchase #4 $210.82   3.586%   $218.38   $218.38   $218.40   $218.40  
  Purchase #5 $225.95   3.836%   $234.6174   $234.62   $234.60   $234.60  
  Purchase #6 $23.62   10.277%   $26.0474   $26.05   $26.05   $26.00  
  Purchase #7 $67.26   11.155%   $74.7629   $74.76   $74.75   $74.80  
  7 purchase totals = $887.47       $950.1719   $950.18   $950.15   $950.20