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	$94.84	5.595%	$100.1463	$100.15	$100.15	$100.10
Purchase #2	$96.91	10.718%	$107.2968	$107.30	$107.30	$107.30
Purchase #3	$29.26	11.862%	$32.7308	$32.73	$32.75	$32.70
Purchase #4	$77.51	6.576%	$82.6071	$82.61	$82.60	$82.60
Purchase #5	$136.79	7.777%	$147.4282	$147.43	$147.45	$147.40
Purchase #6	$247.38	6.840%	$264.3008	$264.30	$264.30	$264.30
Purchase #7	$57.90	3.555%	$59.9583	$59.96	$59.95	$60.00
7 purchase totals =	$740.59		$794.4683	$794.48	$794.50	$794.40