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 $61.72   12.393%   $69.369   $69.37   $69.35   $69.40  
  Purchase #2 $224.79   13.708%   $255.6042   $255.60   $255.60   $255.60  
  Purchase #3 $91.28   7.680%   $98.2903   $98.29   $98.30   $98.30  
  Purchase #4 $156.25   9.588%   $171.2313   $171.23   $171.25   $171.20  
  Purchase #5 $186.88   5.569%   $197.2873   $197.29   $197.30   $197.30  
  Purchase #6 $107.26   4.719%   $112.3216   $112.32   $112.30   $112.30  
  Purchase #7 $232.35   7.668%   $250.1666   $250.17   $250.15   $250.20  
  7 purchase totals = $1,060.53       $1,154.2703   $1,154.27   $1,154.25   $1,154.30