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	$99.36	12.108%	$111.3905	$111.39	$111.40	$111.40
Purchase #2	$74.64	5.136%	$78.4735	$78.47	$78.45	$78.50
Purchase #3	$73.33	13.268%	$83.0594	$83.06	$83.05	$83.10
Purchase #4	$110.52	7.873%	$119.2212	$119.22	$119.20	$119.20
Purchase #5	$223.60	4.740%	$234.1986	$234.20	$234.20	$234.20
Purchase #6	$52.63	13.801%	$59.8935	$59.89	$59.90	$59.90
Purchase #7	$6.84	7.841%	$7.3763	$7.38	$7.40	$7.40
7 purchase totals =	$640.92		$693.6130	$693.61	$693.60	$693.70