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 $232.47   3.134%   $239.7556   $239.76   $239.75   $239.80  
  Purchase #2 $167.28   13.798%   $190.3613   $190.36   $190.35   $190.40  
  Purchase #3 $115.28   4.465%   $120.4273   $120.43   $120.45   $120.40  
  Purchase #4 $242.88   13.323%   $275.2389   $275.24   $275.25   $275.20  
  Purchase #5 $190.53   11.587%   $212.6067   $212.61   $212.60   $212.60  
  Purchase #6 $119.89   5.623%   $126.6314   $126.63   $126.65   $126.60  
  Purchase #7 $185.81   10.818%   $205.9109   $205.91   $205.90   $205.90  
  7 purchase totals = $1,254.14       $1,370.9321   $1,370.94   $1,370.95   $1,370.90