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 $229.84   4.319%   $239.7668   $239.77   $239.75   $239.80  
  Purchase #2 $57.60   8.322%   $62.3935   $62.39   $62.40   $62.40  
  Purchase #3 $156.65   6.863%   $167.4009   $167.40   $167.40   $167.40  
  Purchase #4 $250.94   12.339%   $281.9035   $281.90   $281.90   $281.90  
  Purchase #5 $164.98   3.332%   $170.4771   $170.48   $170.50   $170.50  
  Purchase #6 $18.51   6.837%   $19.7755   $19.78   $19.80   $19.80  
  Purchase #7 $69.30   4.737%   $72.5827   $72.58   $72.60   $72.60  
  7 purchase totals = $947.82       $1,014.3000   $1,014.30   $1,014.35   $1,014.40