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 $250.35   8.411%   $271.4069   $271.41   $271.40   $271.40  
  Purchase #2 $189.81   12.390%   $213.3275   $213.33   $213.35   $213.30  
  Purchase #3 $101.30   7.717%   $109.1173   $109.12   $109.10   $109.10  
  Purchase #4 $225.73   4.116%   $235.021   $235.02   $235.00   $235.00  
  Purchase #5 $51.59   5.474%   $54.414   $54.41   $54.40   $54.40  
  Purchase #6 $118.67   4.684%   $124.2285   $124.23   $124.25   $124.20  
  Purchase #7 $228.79   8.739%   $248.784   $248.78   $248.80   $248.80  
  7 purchase totals = $1,166.24       $1,256.2992   $1,256.30   $1,256.30   $1,256.20