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	$178.31	4.485%	$186.3072	$186.31	$186.30	$186.30
Purchase #2	$130.40	8.407%	$141.3627	$141.36	$141.35	$141.40
Purchase #3	$39.77	4.369%	$41.5076	$41.51	$41.50	$41.50
Purchase #4	$191.93	4.315%	$200.2118	$200.21	$200.20	$200.20
Purchase #5	$119.61	9.646%	$131.1476	$131.15	$131.15	$131.10
Purchase #6	$163.95	13.477%	$186.0455	$186.05	$186.05	$186.00
Purchase #7	$31.60	5.827%	$33.4413	$33.44	$33.45	$33.40
7 purchase totals =	$855.57		$920.0237	$920.03	$920.00	$919.90