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 $237.73   4.277%   $247.8977   $247.90   $247.90   $247.90  
  Purchase #2 $204.28   10.367%   $225.4577   $225.46   $225.45   $225.50  
  Purchase #3 $249.51   4.183%   $259.947   $259.95   $259.95   $259.90  
  Purchase #4 $22.79   7.120%   $24.4126   $24.41   $24.40   $24.40  
  Purchase #5 $62.84   11.108%   $69.8203   $69.82   $69.80   $69.80  
  Purchase #6 $62.27   8.664%   $67.6651   $67.67   $67.65   $67.70  
  Purchase #7 $64.63   4.139%   $67.305   $67.31   $67.30   $67.30  
  7 purchase totals = $904.05       $962.5054   $962.52   $962.45   $962.50