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	$143.79	3.561%	$148.9104	$148.91	$148.90	$148.90
Purchase #2	$56.90	13.649%	$64.6663	$64.67	$64.65	$64.70
Purchase #3	$114.28	11.805%	$127.7708	$127.77	$127.75	$127.80
Purchase #4	$226.48	3.432%	$234.2528	$234.25	$234.25	$234.30
Purchase #5	$30.28	10.318%	$33.4043	$33.40	$33.40	$33.40
Purchase #6	$127.50	7.694%	$137.3099	$137.31	$137.30	$137.30
Purchase #7	$165.41	12.279%	$185.7207	$185.72	$185.70	$185.70
7 purchase totals =	$864.64		$932.0352	$932.03	$931.95	$932.10