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 $86.75   8.661%   $94.2634   $94.26   $94.25   $94.30  
  Purchase #2 $184.88   13.537%   $209.9072   $209.91   $209.90   $209.90  
  Purchase #3 $194.69   3.232%   $200.9824   $200.98   $201.00   $201.00  
  Purchase #4 $196.47   5.354%   $206.989   $206.99   $207.00   $207.00  
  Purchase #5 $169.55   3.531%   $175.5368   $175.54   $175.55   $175.50  
  Purchase #6 $221.84   11.844%   $248.1147   $248.11   $248.10   $248.10  
  Purchase #7 $115.80   4.697%   $121.2391   $121.24   $121.25   $121.20  
  7 purchase totals = $1,169.98       $1,257.0326   $1,257.03   $1,257.05   $1,257.00