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	$241.96	13.700%	$275.1085	$275.11	$275.10	$275.10
Purchase #2	$175.91	3.396%	$181.8839	$181.88	$181.90	$181.90
Purchase #3	$37.86	5.426%	$39.9143	$39.91	$39.90	$39.90
Purchase #4	$90.62	12.505%	$101.952	$101.95	$101.95	$102.00
Purchase #5	$95.72	10.860%	$106.1152	$106.12	$106.10	$106.10
Purchase #6	$25.84	11.186%	$28.7305	$28.73	$28.75	$28.70
Purchase #7	$93.36	13.231%	$105.7125	$105.71	$105.70	$105.70
7 purchase totals =	$761.27		$839.4169	$839.41	$839.40	$839.40