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 $42.29   12.594%   $47.616   $47.62   $47.60   $47.60  
  Purchase #2 $172.62   11.597%   $192.6387   $192.64   $192.65   $192.60  
  Purchase #3 $92.83   3.343%   $95.9333   $95.93   $95.95   $95.90  
  Purchase #4 $185.65   12.781%   $209.3779   $209.38   $209.40   $209.40  
  Purchase #5 $76.90   5.764%   $81.3325   $81.33   $81.35   $81.30  
  Purchase #6 $226.80   11.162%   $252.1154   $252.12   $252.10   $252.10  
  Purchase #7 $161.51   3.620%   $167.3567   $167.36   $167.35   $167.40  
  7 purchase totals = $958.60       $1,046.3705   $1,046.38   $1,046.40   $1,046.30