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 $129.40   12.768%   $145.9218   $145.92   $145.90   $145.90  
  Purchase #2 $121.30   4.690%   $126.989   $126.99   $127.00   $127.00  
  Purchase #3 $39.59   3.394%   $40.9337   $40.93   $40.95   $40.90  
  Purchase #4 $11.81   9.347%   $12.9139   $12.91   $12.90   $12.90  
  Purchase #5 $151.72   6.384%   $161.4058   $161.41   $161.40   $161.40  
  Purchase #6 $140.64   12.160%   $157.7418   $157.74   $157.75   $157.70  
  Purchase #7 $142.27   10.565%   $157.3008   $157.30   $157.30   $157.30  
  7 purchase totals = $736.73       $803.2068   $803.20   $803.20   $803.10