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 $154.47   11.221%   $171.8031   $171.80   $171.80   $171.80  
  Purchase #2 $85.90   12.483%   $96.6229   $96.62   $96.60   $96.60  
  Purchase #3 $132.37   4.446%   $138.2552   $138.26   $138.25   $138.30  
  Purchase #4 $124.94   9.174%   $136.402   $136.40   $136.40   $136.40  
  Purchase #5 $120.63   13.459%   $136.8656   $136.87   $136.85   $136.90  
  Purchase #6 $236.32   5.572%   $249.4878   $249.49   $249.50   $249.50  
  Purchase #7 $90.71   4.676%   $94.9516   $94.95   $94.95   $95.00  
  7 purchase totals = $945.34       $1,024.3882   $1,024.39   $1,024.35   $1,024.50