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	$69.54	4.222%	$72.476	$72.48	$72.50	$72.50
Purchase #2	$199.98	3.164%	$206.3074	$206.31	$206.30	$206.30
Purchase #3	$58.31	4.396%	$60.8733	$60.87	$60.85	$60.90
Purchase #4	$178.35	13.830%	$203.0158	$203.02	$203.00	$203.00
Purchase #5	$167.96	10.830%	$186.1501	$186.15	$186.15	$186.20
Purchase #6	$55.65	6.429%	$59.2277	$59.23	$59.25	$59.20
Purchase #7	$77.54	6.836%	$82.8406	$82.84	$82.85	$82.80
7 purchase totals =	$807.33		$870.8909	$870.90	$870.90	$870.90