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	$238.66	6.754%	$254.7791	$254.78	$254.80	$254.80
Purchase #2	$80.54	3.694%	$83.5151	$83.52	$83.50	$83.50
Purchase #3	$136.35	11.535%	$152.078	$152.08	$152.10	$152.10
Purchase #4	$166.76	10.534%	$184.3265	$184.33	$184.35	$184.30
Purchase #5	$147.63	6.390%	$157.0636	$157.06	$157.05	$157.10
Purchase #6	$37.41	13.283%	$42.3792	$42.38	$42.40	$42.40
Purchase #7	$129.77	11.817%	$145.1049	$145.10	$145.10	$145.10
7 purchase totals =	$937.12		$1,019.2464	$1,019.25	$1,019.30	$1,019.30