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	$30.63	5.276%	$32.246	$32.25	$32.25	$32.20
Purchase #2	$130.42	10.760%	$144.4532	$144.45	$144.45	$144.50
Purchase #3	$25.69	11.678%	$28.6901	$28.69	$28.70	$28.70
Purchase #4	$31.49	12.114%	$35.3047	$35.30	$35.30	$35.30
Purchase #5	$91.56	6.483%	$97.4958	$97.50	$97.50	$97.50
Purchase #6	$118.79	13.333%	$134.6283	$134.63	$134.65	$134.60
Purchase #7	$76.36	7.492%	$82.0809	$82.08	$82.10	$82.10
7 purchase totals =	$504.94		$554.8990	$554.90	$554.95	$554.90