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	$173.34	9.464%	$189.7449	$189.74	$189.75	$189.70
Purchase #2	$162.30	4.217%	$169.1442	$169.14	$169.15	$169.10
Purchase #3	$55.83	9.715%	$61.2539	$61.25	$61.25	$61.30
Purchase #4	$25.99	8.388%	$28.17	$28.17	$28.15	$28.20
Purchase #5	$159.45	8.400%	$172.8438	$172.84	$172.85	$172.80
Purchase #6	$53.35	11.386%	$59.4244	$59.42	$59.40	$59.40
Purchase #7	$218.46	9.660%	$239.5632	$239.56	$239.55	$239.60
7 purchase totals =	$848.72		$920.1444	$920.12	$920.10	$920.10