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	$138.44	12.793%	$156.1506	$156.15	$156.15	$156.20
Purchase #2	$139.95	10.460%	$154.5888	$154.59	$154.60	$154.60
Purchase #3	$241.67	10.740%	$267.6254	$267.63	$267.65	$267.60
Purchase #4	$113.64	9.573%	$124.5188	$124.52	$124.50	$124.50
Purchase #5	$120.96	7.505%	$130.038	$130.04	$130.05	$130.00
Purchase #6	$169.32	12.572%	$190.6069	$190.61	$190.60	$190.60
Purchase #7	$50.39	3.317%	$52.0614	$52.06	$52.05	$52.10
7 purchase totals =	$974.37		$1,075.5899	$1,075.60	$1,075.60	$1,075.60