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 $53.46   6.359%   $56.8595   $56.86   $56.85   $56.90  
  Purchase #2 $185.87   4.854%   $194.8921   $194.89   $194.90   $194.90  
  Purchase #3 $114.85   5.538%   $121.2104   $121.21   $121.20   $121.20  
  Purchase #4 $230.38   9.214%   $251.6072   $251.61   $251.60   $251.60  
  Purchase #5 $165.72   6.149%   $175.9101   $175.91   $175.90   $175.90  
  Purchase #6 $159.93   10.236%   $176.3004   $176.30   $176.30   $176.30  
  Purchase #7 $148.98   11.266%   $165.7641   $165.76   $165.75   $165.80  
  7 purchase totals = $1,059.19       $1,142.5438   $1,142.54   $1,142.50   $1,142.60