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	$165.54	12.764%	$186.6695	$186.67	$186.65	$186.70
Purchase #2	$35.32	9.247%	$38.586	$38.59	$38.60	$38.60
Purchase #3	$54.84	8.296%	$59.3895	$59.39	$59.40	$59.40
Purchase #4	$198.70	11.487%	$221.5247	$221.52	$221.50	$221.50
Purchase #5	$65.52	12.800%	$73.9066	$73.91	$73.90	$73.90
Purchase #6	$144.78	3.547%	$149.9153	$149.92	$149.90	$149.90
Purchase #7	$160.47	6.333%	$170.6326	$170.63	$170.65	$170.60
7 purchase totals =	$825.17		$900.6242	$900.63	$900.60	$900.60