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	$166.75	12.741%	$187.9956	$188.00	$188.00	$188.00
Purchase #2	$37.43	5.663%	$39.5497	$39.55	$39.55	$39.50
Purchase #3	$130.50	6.605%	$139.1195	$139.12	$139.10	$139.10
Purchase #4	$70.66	10.861%	$78.3344	$78.33	$78.35	$78.30
Purchase #5	$202.57	11.356%	$225.5738	$225.57	$225.55	$225.60
Purchase #6	$238.72	13.137%	$270.0806	$270.08	$270.10	$270.10
Purchase #7	$92.37	10.424%	$101.9986	$102.00	$102.00	$102.00
7 purchase totals =	$939.00		$1,042.6522	$1,042.65	$1,042.65	$1,042.60