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 $54.37   8.493%   $58.9876   $58.99   $59.00   $59.00  
  Purchase #2 $157.37   6.348%   $167.3598   $167.36   $167.35   $167.40  
  Purchase #3 $19.82   13.463%   $22.4884   $22.49   $22.50   $22.50  
  Purchase #4 $15.82   3.327%   $16.3463   $16.35   $16.35   $16.30  
  Purchase #5 $209.53   6.233%   $222.59   $222.59   $222.60   $222.60  
  Purchase #6 $109.56   3.188%   $113.0528   $113.05   $113.05   $113.10  
  Purchase #7 $31.91   7.257%   $34.2257   $34.23   $34.25   $34.20  
  7 purchase totals = $598.38       $635.0506   $635.06   $635.10   $635.10