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	$165.57	3.501%	$171.3666	$171.37	$171.35	$171.40
Purchase #2	$159.81	3.597%	$165.5584	$165.56	$165.55	$165.60
Purchase #3	$72.70	11.784%	$81.267	$81.27	$81.25	$81.30
Purchase #4	$207.63	10.411%	$229.2464	$229.25	$229.25	$229.20
Purchase #5	$86.89	11.666%	$97.0266	$97.03	$97.05	$97.00
Purchase #6	$137.94	6.265%	$146.5819	$146.58	$146.60	$146.60
Purchase #7	$72.77	6.279%	$77.3392	$77.34	$77.35	$77.30
7 purchase totals =	$903.31		$968.3861	$968.40	$968.40	$968.40