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 $155.48   7.414%   $167.0073   $167.01   $167.00   $167.00  
  Purchase #2 $230.64   5.190%   $242.6102   $242.61   $242.60   $242.60  
  Purchase #3 $79.44   7.389%   $85.3098   $85.31   $85.30   $85.30  
  Purchase #4 $107.25   7.187%   $114.9581   $114.96   $114.95   $115.00  
  Purchase #5 $237.82   3.362%   $245.8155   $245.82   $245.80   $245.80  
  Purchase #6 $51.53   9.784%   $56.5717   $56.57   $56.55   $56.60  
  Purchase #7 $65.53   11.346%   $72.965   $72.97   $72.95   $73.00  
  7 purchase totals = $927.69       $985.2376   $985.25   $985.15   $985.30