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 $175.74   8.755%   $191.126   $191.13   $191.15   $191.10  
  Purchase #2 $14.61   11.505%   $16.2909   $16.29   $16.30   $16.30  
  Purchase #3 $175.45   11.457%   $195.5513   $195.55   $195.55   $195.60  
  Purchase #4 $76.87   8.425%   $83.3463   $83.35   $83.35   $83.30  
  Purchase #5 $59.59   6.686%   $63.5742   $63.57   $63.55   $63.60  
  Purchase #6 $179.40   4.702%   $187.8354   $187.84   $187.85   $187.80  
  Purchase #7 $235.25   5.762%   $248.8051   $248.81   $248.80   $248.80  
  7 purchase totals = $916.91       $986.5292   $986.54   $986.55   $986.50