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 $234.95   7.689%   $253.0153   $253.02   $253.00   $253.00  
  Purchase #2 $46.96   11.157%   $52.1993   $52.20   $52.20   $52.20  
  Purchase #3 $42.83   4.302%   $44.6725   $44.67   $44.65   $44.70  
  Purchase #4 $227.60   8.635%   $247.2533   $247.25   $247.25   $247.30  
  Purchase #5 $164.92   13.796%   $187.6724   $187.67   $187.65   $187.70  
  Purchase #6 $114.32   12.821%   $128.977   $128.98   $129.00   $129.00  
  Purchase #7 $208.27   11.830%   $232.9083   $232.91   $232.90   $232.90  
  7 purchase totals = $1,039.85       $1,146.6981   $1,146.70   $1,146.65   $1,146.80