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 $167.64   12.658%   $188.8599   $188.86   $188.85   $188.90  
  Purchase #2 $84.68   10.566%   $93.6273   $93.63   $93.65   $93.60  
  Purchase #3 $35.64   4.835%   $37.3632   $37.36   $37.35   $37.40  
  Purchase #4 $175.69   10.573%   $194.2657   $194.27   $194.25   $194.30  
  Purchase #5 $235.98   8.653%   $256.3993   $256.40   $256.40   $256.40  
  Purchase #6 $119.61   11.244%   $133.0589   $133.06   $133.05   $133.10  
  Purchase #7 $154.98   10.716%   $171.5877   $171.59   $171.60   $171.60  
  7 purchase totals = $974.22       $1,075.1620   $1,075.17   $1,075.15   $1,075.30