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	$106.54	7.487%	$114.5166	$114.52	$114.50	$114.50
Purchase #2	$136.68	9.628%	$149.8396	$149.84	$149.85	$149.80
Purchase #3	$78.72	12.116%	$88.2577	$88.26	$88.25	$88.30
Purchase #4	$212.47	5.229%	$223.5801	$223.58	$223.60	$223.60
Purchase #5	$144.89	4.157%	$150.9131	$150.91	$150.90	$150.90
Purchase #6	$90.99	9.161%	$99.3256	$99.33	$99.35	$99.30
Purchase #7	$36.29	3.629%	$37.607	$37.61	$37.60	$37.60
7 purchase totals =	$806.58		$864.0397	$864.05	$864.05	$864.00