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 $131.90   5.585%   $139.2666   $139.27   $139.25   $139.30  
  Purchase #2 $203.63   4.495%   $212.7832   $212.78   $212.80   $212.80  
  Purchase #3 $167.34   9.320%   $182.9361   $182.94   $182.95   $182.90  
  Purchase #4 $148.93   13.832%   $169.53   $169.53   $169.55   $169.50  
  Purchase #5 $23.86   9.556%   $26.1401   $26.14   $26.15   $26.10  
  Purchase #6 $238.71   12.118%   $267.6369   $267.64   $267.65   $267.60  
  Purchase #7 $44.66   12.736%   $50.3479   $50.35   $50.35   $50.30  
  7 purchase totals = $959.03       $1,048.6408   $1,048.65   $1,048.70   $1,048.50