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 $143.95   12.253%   $161.5882   $161.59   $161.60   $161.60  
  Purchase #2 $133.41   8.834%   $145.1954   $145.20   $145.20   $145.20  
  Purchase #3 $10.80   7.371%   $11.5961   $11.60   $11.60   $11.60  
  Purchase #4 $128.57   8.493%   $139.4895   $139.49   $139.50   $139.50  
  Purchase #5 $196.71   11.762%   $219.847   $219.85   $219.85   $219.80  
  Purchase #6 $194.60   13.187%   $220.2619   $220.26   $220.25   $220.30  
  Purchase #7 $213.69   9.130%   $233.1999   $233.20   $233.20   $233.20  
  7 purchase totals = $1,021.73       $1,131.1780   $1,131.19   $1,131.20   $1,131.20