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	$234.59	3.496%	$242.7913	$242.79	$242.80	$242.80
Purchase #2	$84.89	6.435%	$90.3527	$90.35	$90.35	$90.40
Purchase #3	$26.73	6.226%	$28.3942	$28.39	$28.40	$28.40
Purchase #4	$26.83	6.575%	$28.5941	$28.59	$28.60	$28.60
Purchase #5	$175.34	4.812%	$183.7774	$183.78	$183.80	$183.80
Purchase #6	$98.47	11.728%	$110.0186	$110.02	$110.00	$110.00
Purchase #7	$109.71	3.870%	$113.9558	$113.96	$113.95	$114.00
7 purchase totals =	$756.56		$797.8841	$797.88	$797.90	$798.00