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	$222.30	3.102%	$229.1957	$229.20	$229.20	$229.20
Purchase #2	$65.93	7.829%	$71.0917	$71.09	$71.10	$71.10
Purchase #3	$160.46	5.578%	$169.4105	$169.41	$169.40	$169.40
Purchase #4	$34.53	13.642%	$39.2406	$39.24	$39.25	$39.20
Purchase #5	$247.73	13.251%	$280.5567	$280.56	$280.55	$280.60
Purchase #6	$110.48	13.610%	$125.5163	$125.52	$125.50	$125.50
Purchase #7	$168.38	9.429%	$184.2566	$184.26	$184.25	$184.30
7 purchase totals =	$1,009.81		$1,099.2681	$1,099.28	$1,099.25	$1,099.30