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 $52.70   4.868%   $55.2654   $55.27   $55.25   $55.30  
  Purchase #2 $140.63   3.127%   $145.0275   $145.03   $145.05   $145.00  
  Purchase #3 $155.80   3.544%   $161.3216   $161.32   $161.30   $161.30  
  Purchase #4 $216.97   3.828%   $225.2756   $225.28   $225.30   $225.30  
  Purchase #5 $12.38   10.127%   $13.6337   $13.63   $13.65   $13.60  
  Purchase #6 $115.95   3.211%   $119.6732   $119.67   $119.65   $119.70  
  Purchase #7 $67.88   11.578%   $75.7391   $75.74   $75.75   $75.70  
  7 purchase totals = $762.31       $795.9361   $795.94   $795.95   $795.90