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 $48.43   12.772%   $54.6155   $54.62   $54.60   $54.60  
  Purchase #2 $119.87   11.498%   $133.6527   $133.65   $133.65   $133.70  
  Purchase #3 $48.40   6.867%   $51.7236   $51.72   $51.70   $51.70  
  Purchase #4 $244.39   10.449%   $269.9263   $269.93   $269.95   $269.90  
  Purchase #5 $66.47   11.695%   $74.2437   $74.24   $74.25   $74.20  
  Purchase #6 $151.92   8.846%   $165.3588   $165.36   $165.35   $165.40  
  Purchase #7 $75.46   9.652%   $82.7434   $82.74   $82.75   $82.70  
  7 purchase totals = $754.94       $832.2640   $832.26   $832.25   $832.20