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	$215.57	3.657%	$223.4534	$223.45	$223.45	$223.50
Purchase #2	$111.39	6.236%	$118.3363	$118.34	$118.35	$118.30
Purchase #3	$33.43	7.593%	$35.9683	$35.97	$35.95	$36.00
Purchase #4	$88.97	12.821%	$100.3768	$100.38	$100.40	$100.40
Purchase #5	$7.62	4.227%	$7.9421	$7.94	$7.95	$7.90
Purchase #6	$36.74	12.436%	$41.309	$41.31	$41.30	$41.30
Purchase #7	$66.94	7.416%	$71.9043	$71.90	$71.90	$71.90
7 purchase totals =	$560.66		$599.2902	$599.29	$599.30	$599.30