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	$55.33	3.863%	$57.4674	$57.47	$57.45	$57.50
Purchase #2	$200.31	13.778%	$227.9087	$227.91	$227.90	$227.90
Purchase #3	$72.41	12.821%	$81.6937	$81.69	$81.70	$81.70
Purchase #4	$179.33	3.178%	$185.0291	$185.03	$185.05	$185.00
Purchase #5	$111.65	12.257%	$125.3349	$125.33	$125.35	$125.30
Purchase #6	$133.60	6.377%	$142.1197	$142.12	$142.10	$142.10
Purchase #7	$93.30	7.414%	$100.2173	$100.22	$100.20	$100.20
7 purchase totals =	$845.93		$919.7708	$919.77	$919.75	$919.70