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 $213.43   13.266%   $241.7436   $241.74   $241.75   $241.70  
  Purchase #2 $96.39   5.121%   $101.3261   $101.33   $101.35   $101.30  
  Purchase #3 $103.61   6.623%   $110.4721   $110.47   $110.45   $110.50  
  Purchase #4 $63.25   7.756%   $68.1557   $68.16   $68.15   $68.20  
  Purchase #5 $19.29   4.542%   $20.1662   $20.17   $20.15   $20.20  
  Purchase #6 $196.90   12.629%   $221.7665   $221.77   $221.75   $221.80  
  Purchase #7 $139.29   5.290%   $146.6584   $146.66   $146.65   $146.70  
  7 purchase totals = $832.16       $910.2886   $910.30   $910.25   $910.40