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 $236.58   3.688%   $245.3051   $245.31   $245.30   $245.30  
  Purchase #2 $175.39   9.248%   $191.6101   $191.61   $191.60   $191.60  
  Purchase #3 $13.52   7.306%   $14.5078   $14.51   $14.50   $14.50  
  Purchase #4 $218.50   5.334%   $230.1548   $230.15   $230.15   $230.20  
  Purchase #5 $69.74   5.833%   $73.8079   $73.81   $73.80   $73.80  
  Purchase #6 $98.61   11.277%   $109.7302   $109.73   $109.75   $109.70  
  Purchase #7 $151.83   11.242%   $168.8987   $168.90   $168.90   $168.90  
  7 purchase totals = $964.17       $1,034.0146   $1,034.02   $1,034.00   $1,034.00