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	$52.30	13.685%	$59.4573	$59.46	$59.45	$59.50
Purchase #2	$136.41	7.770%	$147.0091	$147.01	$147.00	$147.00
Purchase #3	$152.29	8.865%	$165.7905	$165.79	$165.80	$165.80
Purchase #4	$235.89	13.821%	$268.4924	$268.49	$268.50	$268.50
Purchase #5	$87.40	6.290%	$92.8975	$92.90	$92.90	$92.90
Purchase #6	$25.66	10.689%	$28.4028	$28.40	$28.40	$28.40
Purchase #7	$127.70	7.359%	$137.0974	$137.10	$137.10	$137.10
7 purchase totals =	$817.65		$899.1470	$899.15	$899.15	$899.20