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 $231.91   5.472%   $244.6001   $244.60   $244.60   $244.60  
  Purchase #2 $73.31   3.437%   $75.8297   $75.83   $75.85   $75.80  
  Purchase #3 $17.61   11.405%   $19.6184   $19.62   $19.60   $19.60  
  Purchase #4 $49.38   12.253%   $55.4305   $55.43   $55.45   $55.40  
  Purchase #5 $122.49   8.394%   $132.7718   $132.77   $132.75   $132.80  
  Purchase #6 $114.70   10.623%   $126.8846   $126.88   $126.90   $126.90  
  Purchase #7 $141.84   6.393%   $150.9078   $150.91   $150.90   $150.90  
  7 purchase totals = $751.24       $806.0429   $806.04   $806.05   $806.00