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	$47.59	6.734%	$50.7947	$50.79	$50.80	$50.80
Purchase #2	$113.98	11.597%	$127.1983	$127.20	$127.20	$127.20
Purchase #3	$165.75	4.673%	$173.4955	$173.50	$173.50	$173.50
Purchase #4	$39.57	13.271%	$44.8213	$44.82	$44.80	$44.80
Purchase #5	$57.42	4.290%	$59.8833	$59.88	$59.90	$59.90
Purchase #6	$137.33	9.771%	$150.7485	$150.75	$150.75	$150.70
Purchase #7	$178.45	13.363%	$202.2963	$202.30	$202.30	$202.30
7 purchase totals =	$740.09		$809.2379	$809.24	$809.25	$809.20