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	$236.82	4.543%	$247.5787	$247.58	$247.60	$247.60
Purchase #2	$240.48	13.808%	$273.6855	$273.69	$273.70	$273.70
Purchase #3	$134.32	12.767%	$151.4686	$151.47	$151.45	$151.50
Purchase #4	$178.76	3.836%	$185.6172	$185.62	$185.60	$185.60
Purchase #5	$115.55	12.599%	$130.1081	$130.11	$130.10	$130.10
Purchase #6	$10.52	3.223%	$10.8591	$10.86	$10.85	$10.90
Purchase #7	$135.62	4.714%	$142.0131	$142.01	$142.00	$142.00
7 purchase totals =	$1,052.07		$1,141.3303	$1,141.34	$1,141.30	$1,141.40