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	$78.35	12.870%	$88.4336	$88.43	$88.45	$88.40
Purchase #2	$156.47	10.489%	$172.8821	$172.88	$172.90	$172.90
Purchase #3	$146.69	6.812%	$156.6825	$156.68	$156.70	$156.70
Purchase #4	$89.97	4.514%	$94.0312	$94.03	$94.05	$94.00
Purchase #5	$125.53	10.648%	$138.8964	$138.90	$138.90	$138.90
Purchase #6	$35.56	6.107%	$37.7316	$37.73	$37.75	$37.70
Purchase #7	$35.58	6.312%	$37.8258	$37.83	$37.85	$37.80
7 purchase totals =	$668.15		$726.4832	$726.48	$726.60	$726.40