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 $231.66   6.410%   $246.5094   $246.51   $246.50   $246.50  
  Purchase #2 $206.60   13.571%   $234.6377   $234.64   $234.65   $234.60  
  Purchase #3 $159.61   4.736%   $167.1691   $167.17   $167.15   $167.20  
  Purchase #4 $236.65   8.741%   $257.3356   $257.34   $257.35   $257.30  
  Purchase #5 $60.71   12.493%   $68.2945   $68.29   $68.30   $68.30  
  Purchase #6 $140.78   7.720%   $151.6482   $151.65   $151.65   $151.60  
  Purchase #7 $56.29   5.182%   $59.2069   $59.21   $59.20   $59.20  
  7 purchase totals = $1,092.30       $1,184.8014   $1,184.81   $1,184.80   $1,184.70