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 $90.82   11.392%   $101.1662   $101.17   $101.15   $101.20  
  Purchase #2 $166.51   5.295%   $175.3267   $175.33   $175.35   $175.30  
  Purchase #3 $110.93   7.247%   $118.9691   $118.97   $118.95   $119.00  
  Purchase #4 $235.59   6.277%   $250.378   $250.38   $250.40   $250.40  
  Purchase #5 $105.33   8.629%   $114.4189   $114.42   $114.40   $114.40  
  Purchase #6 $122.68   8.563%   $133.1851   $133.19   $133.20   $133.20  
  Purchase #7 $191.74   10.675%   $212.2082   $212.21   $212.20   $212.20  
  7 purchase totals = $1,023.60       $1,105.6522   $1,105.67   $1,105.65   $1,105.70