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 $58.97   13.543%   $66.9563   $66.96   $66.95   $67.00  
  Purchase #2 $85.80   3.634%   $88.918   $88.92   $88.90   $88.90  
  Purchase #3 $74.82   11.235%   $83.226   $83.23   $83.25   $83.20  
  Purchase #4 $194.57   7.671%   $209.4955   $209.50   $209.50   $209.50  
  Purchase #5 $133.39   13.278%   $151.1015   $151.10   $151.10   $151.10  
  Purchase #6 $175.91   4.539%   $183.8946   $183.89   $183.90   $183.90  
  Purchase #7 $61.54   11.540%   $68.6417   $68.64   $68.65   $68.60  
  7 purchase totals = $785.00       $852.2336   $852.24   $852.25   $852.20