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	$78.61	10.868%	$87.1533	$87.15	$87.15	$87.20
Purchase #2	$228.72	6.197%	$242.8938	$242.89	$242.90	$242.90
Purchase #3	$16.85	9.818%	$18.5043	$18.50	$18.50	$18.50
Purchase #4	$98.64	7.113%	$105.6563	$105.66	$105.65	$105.70
Purchase #5	$71.81	9.324%	$78.5056	$78.51	$78.50	$78.50
Purchase #6	$6.63	10.230%	$7.3082	$7.31	$7.30	$7.30
Purchase #7	$54.40	9.169%	$59.3879	$59.39	$59.40	$59.40
7 purchase totals =	$555.66		$599.4094	$599.41	$599.40	$599.50