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 $61.92   7.771%   $66.7318   $66.73   $66.75   $66.70  
  Purchase #2 $146.65   13.138%   $165.9169   $165.92   $165.90   $165.90  
  Purchase #3 $174.55   11.224%   $194.1415   $194.14   $194.15   $194.10  
  Purchase #4 $104.81   7.129%   $112.2819   $112.28   $112.30   $112.30  
  Purchase #5 $198.32   3.627%   $205.5131   $205.51   $205.50   $205.50  
  Purchase #6 $182.82   12.791%   $206.2045   $206.20   $206.20   $206.20  
  Purchase #7 $74.52   9.216%   $81.3878   $81.39   $81.40   $81.40  
  7 purchase totals = $943.59       $1,032.1775   $1,032.17   $1,032.20   $1,032.10