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 $83.43   11.275%   $92.8367   $92.84   $92.85   $92.80  
  Purchase #2 $109.76   8.264%   $118.8306   $118.83   $118.85   $118.80  
  Purchase #3 $223.28   8.614%   $242.5133   $242.51   $242.50   $242.50  
  Purchase #4 $155.89   8.592%   $169.2841   $169.28   $169.30   $169.30  
  Purchase #5 $126.33   12.430%   $142.0328   $142.03   $142.05   $142.00  
  Purchase #6 $186.36   3.268%   $192.4502   $192.45   $192.45   $192.50  
  Purchase #7 $230.25   6.666%   $245.5985   $245.60   $245.60   $245.60  
  7 purchase totals = $1,115.30       $1,203.5462   $1,203.54   $1,203.60   $1,203.50