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	$118.66	4.693%	$124.2287	$124.23	$124.25	$124.20
Purchase #2	$250.60	11.415%	$279.206	$279.21	$279.20	$279.20
Purchase #3	$40.55	5.107%	$42.6209	$42.62	$42.60	$42.60
Purchase #4	$225.25	8.109%	$243.5155	$243.52	$243.50	$243.50
Purchase #5	$76.50	11.808%	$85.5331	$85.53	$85.55	$85.50
Purchase #6	$22.80	12.425%	$25.6329	$25.63	$25.65	$25.60
Purchase #7	$106.35	5.821%	$112.5406	$112.54	$112.55	$112.50
7 purchase totals =	$840.71		$913.2777	$913.28	$913.30	$913.10