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 $134.72   13.337%   $152.6876   $152.69   $152.70   $152.70  
  Purchase #2 $176.70   10.554%   $195.3489   $195.35   $195.35   $195.30  
  Purchase #3 $157.99   10.597%   $174.7322   $174.73   $174.75   $174.70  
  Purchase #4 $14.73   12.147%   $16.5193   $16.52   $16.50   $16.50  
  Purchase #5 $134.82   8.672%   $146.5116   $146.51   $146.50   $146.50  
  Purchase #6 $11.90   8.842%   $12.9522   $12.95   $12.95   $13.00  
  Purchase #7 $62.48   3.707%   $64.7961   $64.80   $64.80   $64.80  
  7 purchase totals = $693.34       $763.5479   $763.55   $763.55   $763.50