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	$155.64	12.361%	$174.8787	$174.88	$174.90	$174.90
Purchase #2	$92.32	4.117%	$96.1208	$96.12	$96.10	$96.10
Purchase #3	$164.59	5.821%	$174.1708	$174.17	$174.15	$174.20
Purchase #4	$128.25	13.347%	$145.3675	$145.37	$145.35	$145.40
Purchase #5	$6.42	10.172%	$7.073	$7.07	$7.05	$7.10
Purchase #6	$39.38	11.560%	$43.9323	$43.93	$43.95	$43.90
Purchase #7	$24.46	11.405%	$27.2497	$27.25	$27.25	$27.20
7 purchase totals =	$611.06		$668.7928	$668.79	$668.75	$668.80