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 $9.85   4.368%   $10.2802   $10.28   $10.30   $10.30  
  Purchase #2 $242.44   3.625%   $251.2285   $251.23   $251.25   $251.20  
  Purchase #3 $151.25   12.548%   $170.2289   $170.23   $170.25   $170.20  
  Purchase #4 $102.49   11.572%   $114.3501   $114.35   $114.35   $114.40  
  Purchase #5 $82.87   9.559%   $90.7915   $90.79   $90.80   $90.80  
  Purchase #6 $119.41   9.695%   $130.9868   $130.99   $131.00   $131.00  
  Purchase #7 $195.95   7.265%   $210.1858   $210.19   $210.20   $210.20  
  7 purchase totals = $904.26       $978.0518   $978.06   $978.15   $978.10