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 $23.93   9.737%   $26.2601   $26.26   $26.25   $26.30  
  Purchase #2 $82.55   7.238%   $88.525   $88.53   $88.55   $88.50  
  Purchase #3 $88.86   12.853%   $100.2812   $100.28   $100.30   $100.30  
  Purchase #4 $223.37   11.386%   $248.8029   $248.80   $248.80   $248.80  
  Purchase #5 $205.69   6.152%   $218.344   $218.34   $218.35   $218.30  
  Purchase #6 $209.46   4.215%   $218.2887   $218.29   $218.30   $218.30  
  Purchase #7 $202.66   11.651%   $226.2719   $226.27   $226.25   $226.30  
  7 purchase totals = $1,036.52       $1,126.7738   $1,126.77   $1,126.80   $1,126.80