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   5.747%   $91.7355   $91.74   $91.75   $91.70  
  Purchase #2 $109.72   11.211%   $122.0207   $122.02   $122.00   $122.00  
  Purchase #3 $149.97   6.296%   $159.4121   $159.41   $159.40   $159.40  
  Purchase #4 $67.94   8.482%   $73.7027   $73.70   $73.70   $73.70  
  Purchase #5 $111.65   5.132%   $117.3799   $117.38   $117.40   $117.40  
  Purchase #6 $123.32   5.234%   $129.7746   $129.77   $129.75   $129.80  
  Purchase #7 $61.59   7.801%   $66.3946   $66.39   $66.40   $66.40  
  7 purchase totals = $710.94       $760.4201   $760.41   $760.40   $760.40