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	$35.70	10.118%	$39.3121	$39.31	$39.30	$39.30
Purchase #2	$89.38	6.142%	$94.8697	$94.87	$94.85	$94.90
Purchase #3	$90.43	9.549%	$99.0652	$99.07	$99.05	$99.10
Purchase #4	$5.71	12.442%	$6.4204	$6.42	$6.40	$6.40
Purchase #5	$168.32	3.671%	$174.499	$174.50	$174.50	$174.50
Purchase #6	$13.74	8.867%	$14.9583	$14.96	$14.95	$15.00
Purchase #7	$110.95	11.447%	$123.6504	$123.65	$123.65	$123.70
7 purchase totals =	$514.23		$552.7751	$552.78	$552.70	$552.90