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	$33.88	3.618%	$35.1058	$35.11	$35.10	$35.10
Purchase #2	$248.94	11.290%	$277.0453	$277.05	$277.05	$277.00
Purchase #3	$95.59	9.265%	$104.4464	$104.45	$104.45	$104.40
Purchase #4	$95.90	5.251%	$100.9357	$100.94	$100.95	$100.90
Purchase #5	$79.77	7.581%	$85.8174	$85.82	$85.80	$85.80
Purchase #6	$190.83	7.378%	$204.9094	$204.91	$204.90	$204.90
Purchase #7	$10.91	10.212%	$12.0241	$12.02	$12.00	$12.00
7 purchase totals =	$755.82		$820.2841	$820.30	$820.25	$820.10