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	$35.72	8.453%	$38.7394	$38.74	$38.75	$38.70
Purchase #2	$146.64	13.110%	$165.8645	$165.86	$165.85	$165.90
Purchase #3	$105.56	5.596%	$111.4671	$111.47	$111.45	$111.50
Purchase #4	$26.84	5.577%	$28.3369	$28.34	$28.35	$28.30
Purchase #5	$160.97	6.705%	$171.763	$171.76	$171.75	$171.80
Purchase #6	$145.82	7.148%	$156.2432	$156.24	$156.25	$156.20
Purchase #7	$116.85	7.564%	$125.6885	$125.69	$125.70	$125.70
7 purchase totals =	$738.40		$798.1026	$798.10	$798.10	$798.10