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 $165.26   10.680%   $182.9098   $182.91   $182.90   $182.90  
  Purchase #2 $248.51   11.691%   $277.5633   $277.56   $277.55   $277.60  
  Purchase #3 $202.38   8.599%   $219.7827   $219.78   $219.80   $219.80  
  Purchase #4 $43.33   9.197%   $47.3151   $47.32   $47.30   $47.30  
  Purchase #5 $68.42   9.864%   $75.1689   $75.17   $75.15   $75.20  
  Purchase #6 $64.63   13.222%   $73.1754   $73.18   $73.20   $73.20  
  Purchase #7 $80.93   13.801%   $92.0991   $92.10   $92.10   $92.10  
  7 purchase totals = $873.46       $968.0143   $968.02   $968.00   $968.10