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 $206.91   13.651%   $235.1553   $235.16   $235.15   $235.20  
  Purchase #2 $205.41   7.507%   $220.8301   $220.83   $220.85   $220.80  
  Purchase #3 $197.89   9.299%   $216.2918   $216.29   $216.30   $216.30  
  Purchase #4 $235.98   3.702%   $244.716   $244.72   $244.70   $244.70  
  Purchase #5 $191.74   10.847%   $212.538   $212.54   $212.55   $212.50  
  Purchase #6 $199.59   13.361%   $226.2572   $226.26   $226.25   $226.30  
  Purchase #7 $168.44   4.783%   $176.4965   $176.50   $176.50   $176.50  
  7 purchase totals = $1,405.96       $1,532.2849   $1,532.30   $1,532.30   $1,532.30