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	$79.71	13.285%	$90.2995	$90.30	$90.30	$90.30
Purchase #2	$87.51	11.623%	$97.6813	$97.68	$97.70	$97.70
Purchase #3	$92.50	13.179%	$104.6906	$104.69	$104.70	$104.70
Purchase #4	$129.96	9.612%	$142.4518	$142.45	$142.45	$142.50
Purchase #5	$34.69	9.449%	$37.9679	$37.97	$37.95	$38.00
Purchase #6	$82.51	8.237%	$89.3063	$89.31	$89.30	$89.30
Purchase #7	$130.72	8.288%	$141.5541	$141.55	$141.55	$141.60
7 purchase totals =	$637.60		$703.9515	$703.95	$703.95	$704.10