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	$149.77	3.654%	$155.2426	$155.24	$155.25	$155.20
Purchase #2	$158.41	3.820%	$164.4613	$164.46	$164.45	$164.50
Purchase #3	$80.57	9.427%	$88.1653	$88.17	$88.15	$88.20
Purchase #4	$67.88	5.846%	$71.8483	$71.85	$71.85	$71.80
Purchase #5	$73.34	7.302%	$78.6953	$78.70	$78.70	$78.70
Purchase #6	$124.67	13.640%	$141.675	$141.68	$141.70	$141.70
Purchase #7	$143.89	11.216%	$160.0287	$160.03	$160.05	$160.00
7 purchase totals =	$798.53		$860.1165	$860.13	$860.15	$860.10