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 $165.62   6.441%   $176.2876   $176.29   $176.30   $176.30  
  Purchase #2 $107.60   11.436%   $119.9051   $119.91   $119.90   $119.90  
  Purchase #3 $199.65   3.660%   $206.9572   $206.96   $206.95   $207.00  
  Purchase #4 $56.52   8.618%   $61.3909   $61.39   $61.40   $61.40  
  Purchase #5 $54.65   8.271%   $59.1701   $59.17   $59.15   $59.20  
  Purchase #6 $197.29   10.274%   $217.5596   $217.56   $217.55   $217.60  
  Purchase #7 $14.26   5.104%   $14.9878   $14.99   $15.00   $15.00  
  7 purchase totals = $795.59       $856.2583   $856.27   $856.25   $856.40