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	$223.61	12.354%	$251.2348	$251.23	$251.25	$251.20
Purchase #2	$101.39	3.179%	$104.6132	$104.61	$104.60	$104.60
Purchase #3	$250.61	11.154%	$278.563	$278.56	$278.55	$278.60
Purchase #4	$243.98	13.657%	$277.3003	$277.30	$277.30	$277.30
Purchase #5	$33.76	6.383%	$35.9149	$35.91	$35.90	$35.90
Purchase #6	$152.28	3.431%	$157.5047	$157.50	$157.50	$157.50
Purchase #7	$37.27	3.823%	$38.6948	$38.69	$38.70	$38.70
7 purchase totals =	$1,042.90		$1,143.8257	$1,143.80	$1,143.80	$1,143.80