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	$154.49	9.274%	$168.8174	$168.82	$168.80	$168.80
Purchase #2	$119.88	7.180%	$128.4874	$128.49	$128.50	$128.50
Purchase #3	$191.57	4.798%	$200.7615	$200.76	$200.75	$200.80
Purchase #4	$128.45	3.688%	$133.1872	$133.19	$133.20	$133.20
Purchase #5	$143.34	11.286%	$159.5174	$159.52	$159.50	$159.50
Purchase #6	$55.95	5.691%	$59.1341	$59.13	$59.15	$59.10
Purchase #7	$228.43	6.183%	$242.5538	$242.55	$242.55	$242.60
7 purchase totals =	$1,022.11		$1,092.4588	$1,092.46	$1,092.45	$1,092.50