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	$98.60	12.290%	$110.7179	$110.72	$110.70	$110.70
Purchase #2	$40.76	7.517%	$43.8239	$43.82	$43.80	$43.80
Purchase #3	$39.52	6.867%	$42.2338	$42.23	$42.25	$42.20
Purchase #4	$156.88	11.301%	$174.609	$174.61	$174.60	$174.60
Purchase #5	$5.45	11.187%	$6.0597	$6.06	$6.05	$6.10
Purchase #6	$176.51	13.370%	$200.1094	$200.11	$200.10	$200.10
Purchase #7	$128.74	4.314%	$134.2938	$134.29	$134.30	$134.30
7 purchase totals =	$646.46		$711.8475	$711.84	$711.80	$711.80