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	$39.72	13.640%	$45.1378	$45.14	$45.15	$45.10
Purchase #2	$233.53	4.416%	$243.8427	$243.84	$243.85	$243.80
Purchase #3	$228.74	11.627%	$255.3356	$255.34	$255.35	$255.30
Purchase #4	$42.26	10.842%	$46.8418	$46.84	$46.85	$46.80
Purchase #5	$19.32	12.791%	$21.7912	$21.79	$21.80	$21.80
Purchase #6	$159.68	4.864%	$167.4468	$167.45	$167.45	$167.40
Purchase #7	$229.48	3.438%	$237.3695	$237.37	$237.35	$237.40
7 purchase totals =	$952.73		$1,017.7654	$1,017.77	$1,017.80	$1,017.60