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	$45.82	9.499%	$50.1724	$50.17	$50.15	$50.20
Purchase #2	$106.82	4.131%	$111.2327	$111.23	$111.25	$111.20
Purchase #3	$41.46	9.124%	$45.2428	$45.24	$45.25	$45.20
Purchase #4	$5.30	4.658%	$5.5469	$5.55	$5.55	$5.50
Purchase #5	$36.99	11.794%	$41.3526	$41.35	$41.35	$41.40
Purchase #6	$210.55	12.650%	$237.1846	$237.18	$237.20	$237.20
Purchase #7	$93.28	9.553%	$102.191	$102.19	$102.20	$102.20
7 purchase totals =	$540.22		$592.9230	$592.91	$592.95	$592.90