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	$134.73	9.345%	$147.3205	$147.32	$147.30	$147.30
Purchase #2	$49.92	11.166%	$55.4941	$55.49	$55.50	$55.50
Purchase #3	$172.77	7.343%	$185.4565	$185.46	$185.45	$185.50
Purchase #4	$230.87	8.420%	$250.3093	$250.31	$250.30	$250.30
Purchase #5	$170.77	8.170%	$184.7219	$184.72	$184.70	$184.70
Purchase #6	$240.98	7.381%	$258.7667	$258.77	$258.75	$258.80
Purchase #7	$167.59	13.867%	$190.8297	$190.83	$190.85	$190.80
7 purchase totals =	$1,167.63		$1,272.8987	$1,272.90	$1,272.85	$1,272.90