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	$145.72	10.613%	$161.1853	$161.19	$161.20	$161.20
Purchase #2	$7.64	3.608%	$7.9157	$7.92	$7.90	$7.90
Purchase #3	$127.81	7.238%	$137.0609	$137.06	$137.05	$137.10
Purchase #4	$152.89	8.134%	$165.3261	$165.33	$165.35	$165.30
Purchase #5	$37.96	12.115%	$42.5589	$42.56	$42.55	$42.60
Purchase #6	$50.52	4.786%	$52.9379	$52.94	$52.95	$52.90
Purchase #7	$17.99	11.333%	$20.0288	$20.03	$20.05	$20.00
7 purchase totals =	$540.53		$587.0136	$587.03	$587.05	$587.00