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 $50.95   8.244%   $55.1503   $55.15   $55.15   $55.20  
  Purchase #2 $214.29   12.874%   $241.8777   $241.88   $241.90   $241.90  
  Purchase #3 $220.94   3.852%   $229.4506   $229.45   $229.45   $229.50  
  Purchase #4 $233.65   4.547%   $244.2741   $244.27   $244.25   $244.30  
  Purchase #5 $70.36   8.113%   $76.0683   $76.07   $76.05   $76.10  
  Purchase #6 $7.46   9.625%   $8.178   $8.18   $8.20   $8.20  
  Purchase #7 $140.59   4.214%   $146.5145   $146.51   $146.50   $146.50  
  7 purchase totals = $938.24       $1,001.5135   $1,001.51   $1,001.50   $1,001.70