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 $149.86   10.591%   $165.7317   $165.73   $165.75   $165.70  
  Purchase #2 $154.73   6.760%   $165.1897   $165.19   $165.20   $165.20  
  Purchase #3 $82.83   12.867%   $93.4877   $93.49   $93.50   $93.50  
  Purchase #4 $247.28   6.241%   $262.7127   $262.71   $262.70   $262.70  
  Purchase #5 $127.32   4.440%   $132.973   $132.97   $132.95   $133.00  
  Purchase #6 $194.75   7.288%   $208.9434   $208.94   $208.95   $208.90  
  Purchase #7 $123.72   5.704%   $130.777   $130.78   $130.80   $130.80  
  7 purchase totals = $1,080.49       $1,159.8152   $1,159.81   $1,159.85   $1,159.80