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 $52.86   9.616%   $57.943   $57.94   $57.95   $57.90  
  Purchase #2 $106.90   10.679%   $118.3159   $118.32   $118.30   $118.30  
  Purchase #3 $118.63   12.610%   $133.5892   $133.59   $133.60   $133.60  
  Purchase #4 $213.30   5.420%   $224.8609   $224.86   $224.85   $224.90  
  Purchase #5 $234.54   6.165%   $248.9994   $249.00   $249.00   $249.00  
  Purchase #6 $177.85   6.702%   $189.7695   $189.77   $189.75   $189.80  
  Purchase #7 $69.46   4.695%   $72.7211   $72.72   $72.70   $72.70  
  7 purchase totals = $973.54       $1,046.1990   $1,046.20   $1,046.15   $1,046.20