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	$75.83	7.819%	$81.7591	$81.76	$81.75	$81.80
Purchase #2	$111.61	12.478%	$125.5367	$125.54	$125.55	$125.50
Purchase #3	$102.30	7.817%	$110.2968	$110.30	$110.30	$110.30
Purchase #4	$145.56	4.494%	$152.1015	$152.10	$152.10	$152.10
Purchase #5	$96.57	5.215%	$101.6061	$101.61	$101.60	$101.60
Purchase #6	$43.71	3.527%	$45.2517	$45.25	$45.25	$45.30
Purchase #7	$117.92	4.479%	$123.2016	$123.20	$123.20	$123.20
7 purchase totals =	$693.50		$739.7535	$739.76	$739.75	$739.80