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 $157.98   10.152%   $174.0181   $174.02   $174.00   $174.00  
  Purchase #2 $142.63   4.821%   $149.5062   $149.51   $149.50   $149.50  
  Purchase #3 $249.45   7.859%   $269.0543   $269.05   $269.05   $269.10  
  Purchase #4 $65.66   11.298%   $73.0783   $73.08   $73.10   $73.10  
  Purchase #5 $90.48   4.801%   $94.8239   $94.82   $94.80   $94.80  
  Purchase #6 $11.86   3.453%   $12.2695   $12.27   $12.25   $12.30  
  Purchase #7 $240.95   8.138%   $260.5585   $260.56   $260.55   $260.60  
  7 purchase totals = $959.01       $1,033.3088   $1,033.31   $1,033.25   $1,033.40