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 $216.62   8.544%   $235.128   $235.13   $235.15   $235.10  
  Purchase #2 $136.82   12.302%   $153.6516   $153.65   $153.65   $153.70  
  Purchase #3 $125.44   6.235%   $133.2612   $133.26   $133.25   $133.30  
  Purchase #4 $78.97   4.717%   $82.695   $82.70   $82.70   $82.70  
  Purchase #5 $109.43   13.232%   $123.9098   $123.91   $123.90   $123.90  
  Purchase #6 $242.82   10.528%   $268.3841   $268.38   $268.40   $268.40  
  Purchase #7 $22.61   3.309%   $23.3582   $23.36   $23.35   $23.40  
  7 purchase totals = $932.71       $1,020.3879   $1,020.39   $1,020.40   $1,020.50