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	$29.91	9.136%	$32.6426	$32.64	$32.65	$32.60
Purchase #2	$124.69	7.197%	$133.6639	$133.66	$133.65	$133.70
Purchase #3	$33.37	11.366%	$37.1628	$37.16	$37.15	$37.20
Purchase #4	$10.77	9.805%	$11.826	$11.83	$11.85	$11.80
Purchase #5	$215.44	11.506%	$240.2285	$240.23	$240.25	$240.20
Purchase #6	$235.89	4.236%	$245.8823	$245.88	$245.90	$245.90
Purchase #7	$35.35	6.390%	$37.6089	$37.61	$37.60	$37.60
7 purchase totals =	$685.42		$739.0150	$739.01	$739.05	$739.00