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	$159.74	7.554%	$171.8068	$171.81	$171.80	$171.80
Purchase #2	$34.90	7.460%	$37.5035	$37.50	$37.50	$37.50
Purchase #3	$114.71	13.604%	$130.3151	$130.32	$130.30	$130.30
Purchase #4	$216.57	3.189%	$223.4764	$223.48	$223.50	$223.50
Purchase #5	$156.66	10.712%	$173.4414	$173.44	$173.45	$173.40
Purchase #6	$114.90	11.358%	$127.9503	$127.95	$127.95	$128.00
Purchase #7	$224.61	8.300%	$243.2526	$243.25	$243.25	$243.30
7 purchase totals =	$1,022.09		$1,107.7461	$1,107.75	$1,107.75	$1,107.80