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 $54.36   3.368%   $56.1908   $56.19   $56.20   $56.20  
  Purchase #2 $190.38   8.748%   $207.0344   $207.03   $207.05   $207.00  
  Purchase #3 $214.89   6.118%   $228.037   $228.04   $228.05   $228.00  
  Purchase #4 $109.94   11.829%   $122.9448   $122.94   $122.95   $122.90  
  Purchase #5 $237.65   3.610%   $246.2292   $246.23   $246.25   $246.20  
  Purchase #6 $131.99   4.600%   $138.0615   $138.06   $138.05   $138.10  
  Purchase #7 $185.25   13.536%   $210.3254   $210.33   $210.35   $210.30  
  7 purchase totals = $1,124.46       $1,208.8231   $1,208.82   $1,208.90   $1,208.70