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	$92.75	11.498%	$103.4144	$103.41	$103.40	$103.40
Purchase #2	$164.56	4.752%	$172.3799	$172.38	$172.40	$172.40
Purchase #3	$90.83	9.557%	$99.5106	$99.51	$99.50	$99.50
Purchase #4	$140.73	13.515%	$159.7497	$159.75	$159.75	$159.70
Purchase #5	$65.26	4.690%	$68.3207	$68.32	$68.30	$68.30
Purchase #6	$40.35	11.305%	$44.9116	$44.91	$44.90	$44.90
Purchase #7	$88.52	6.813%	$94.5509	$94.55	$94.55	$94.60
7 purchase totals =	$683.00		$742.8378	$742.83	$742.80	$742.80