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 $32.41   6.614%   $34.5536   $34.55   $34.55   $34.60  
  Purchase #2 $119.42   11.359%   $132.9849   $132.98   $133.00   $133.00  
  Purchase #3 $5.63   8.671%   $6.1182   $6.12   $6.10   $6.10  
  Purchase #4 $165.99   4.654%   $173.7152   $173.72   $173.70   $173.70  
  Purchase #5 $107.64   9.745%   $118.1295   $118.13   $118.15   $118.10  
  Purchase #6 $41.73   7.202%   $44.7354   $44.74   $44.75   $44.70  
  Purchase #7 $141.37   13.797%   $160.8748   $160.87   $160.85   $160.90  
  7 purchase totals = $614.19       $671.1116   $671.11   $671.10   $671.10