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	$39.31	8.129%	$42.5055	$42.51	$42.50	$42.50
Purchase #2	$110.42	9.124%	$120.4947	$120.49	$120.50	$120.50
Purchase #3	$130.56	13.520%	$148.2117	$148.21	$148.20	$148.20
Purchase #4	$174.39	4.640%	$182.4817	$182.48	$182.50	$182.50
Purchase #5	$18.72	8.527%	$20.3163	$20.32	$20.30	$20.30
Purchase #6	$151.64	8.865%	$165.0829	$165.08	$165.10	$165.10
Purchase #7	$32.65	9.523%	$35.7593	$35.76	$35.75	$35.80
7 purchase totals =	$657.69		$714.8521	$714.85	$714.85	$714.90