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	$72.74	10.230%	$80.1813	$80.18	$80.20	$80.20
Purchase #2	$219.82	8.448%	$238.3904	$238.39	$238.40	$238.40
Purchase #3	$73.47	6.661%	$78.3638	$78.36	$78.35	$78.40
Purchase #4	$62.95	10.146%	$69.3369	$69.34	$69.35	$69.30
Purchase #5	$91.96	11.513%	$102.5474	$102.55	$102.55	$102.50
Purchase #6	$45.42	7.735%	$48.9332	$48.93	$48.95	$48.90
Purchase #7	$56.67	8.323%	$61.3866	$61.39	$61.40	$61.40
7 purchase totals =	$623.03		$679.1396	$679.14	$679.20	$679.10