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 $44.29   5.754%   $46.8384   $46.84   $46.85   $46.80  
  Purchase #2 $117.98   9.651%   $129.3662   $129.37   $129.35   $129.40  
  Purchase #3 $184.34   8.702%   $200.3813   $200.38   $200.40   $200.40  
  Purchase #4 $18.45   5.733%   $19.5077   $19.51   $19.50   $19.50  
  Purchase #5 $196.68   7.222%   $210.8842   $210.88   $210.90   $210.90  
  Purchase #6 $27.89   9.541%   $30.551   $30.55   $30.55   $30.60  
  Purchase #7 $220.26   8.713%   $239.4513   $239.45   $239.45   $239.50  
  7 purchase totals = $809.89       $876.9801   $876.98   $877.00   $877.10