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	$51.44	5.658%	$54.3505	$54.35	$54.35	$54.40
Purchase #2	$123.29	13.487%	$139.9181	$139.92	$139.90	$139.90
Purchase #3	$110.97	12.850%	$125.2296	$125.23	$125.25	$125.20
Purchase #4	$10.46	12.186%	$11.7347	$11.73	$11.75	$11.70
Purchase #5	$112.48	3.817%	$116.7734	$116.77	$116.75	$116.80
Purchase #6	$165.74	4.697%	$173.5248	$173.52	$173.50	$173.50
Purchase #7	$69.28	13.145%	$78.3869	$78.39	$78.40	$78.40
7 purchase totals =	$643.66		$699.9180	$699.91	$699.90	$699.90