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	$99.75	9.526%	$109.2522	$109.25	$109.25	$109.30
Purchase #2	$10.56	11.782%	$11.8042	$11.80	$11.80	$11.80
Purchase #3	$22.71	10.781%	$25.1584	$25.16	$25.15	$25.20
Purchase #4	$248.74	10.777%	$275.5467	$275.55	$275.55	$275.50
Purchase #5	$67.97	13.679%	$77.2676	$77.27	$77.25	$77.30
Purchase #6	$93.73	3.800%	$97.2917	$97.29	$97.30	$97.30
Purchase #7	$71.27	10.536%	$78.779	$78.78	$78.80	$78.80
7 purchase totals =	$614.73		$675.0998	$675.10	$675.10	$675.20