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	$32.73	4.393%	$34.1678	$34.17	$34.15	$34.20
Purchase #2	$58.33	5.859%	$61.7476	$61.75	$61.75	$61.70
Purchase #3	$108.60	11.278%	$120.8479	$120.85	$120.85	$120.80
Purchase #4	$34.83	10.614%	$38.5269	$38.53	$38.55	$38.50
Purchase #5	$89.92	10.682%	$99.5253	$99.53	$99.55	$99.50
Purchase #6	$68.97	3.698%	$71.5205	$71.52	$71.50	$71.50
Purchase #7	$119.25	8.801%	$129.7452	$129.75	$129.75	$129.70
7 purchase totals =	$512.63		$556.0812	$556.10	$556.10	$555.90