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	$138.89	12.600%	$156.3901	$156.39	$156.40	$156.40
Purchase #2	$117.45	6.579%	$125.177	$125.18	$125.20	$125.20
Purchase #3	$115.52	13.767%	$131.4236	$131.42	$131.40	$131.40
Purchase #4	$13.96	4.331%	$14.5646	$14.56	$14.55	$14.60
Purchase #5	$59.98	6.800%	$64.0586	$64.06	$64.05	$64.10
Purchase #6	$99.31	6.276%	$105.5427	$105.54	$105.55	$105.50
Purchase #7	$138.84	3.451%	$143.6314	$143.63	$143.65	$143.60
7 purchase totals =	$683.95		$740.7880	$740.78	$740.80	$740.80