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	$70.74	12.300%	$79.441	$79.44	$79.45	$79.40
Purchase #2	$93.78	9.715%	$102.8907	$102.89	$102.90	$102.90
Purchase #3	$123.58	3.490%	$127.8929	$127.89	$127.90	$127.90
Purchase #4	$159.83	5.763%	$169.041	$169.04	$169.05	$169.00
Purchase #5	$11.51	5.237%	$12.1128	$12.11	$12.10	$12.10
Purchase #6	$31.47	5.398%	$33.1688	$33.17	$33.15	$33.20
Purchase #7	$49.73	8.550%	$53.9819	$53.98	$54.00	$54.00
7 purchase totals =	$540.64		$578.5291	$578.52	$578.55	$578.50