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	$134.85	12.552%	$151.7764	$151.78	$151.80	$151.80
Purchase #2	$12.25	3.715%	$12.7051	$12.71	$12.70	$12.70
Purchase #3	$38.48	11.507%	$42.9079	$42.91	$42.90	$42.90
Purchase #4	$16.69	5.151%	$17.5497	$17.55	$17.55	$17.50
Purchase #5	$105.84	12.345%	$118.9059	$118.91	$118.90	$118.90
Purchase #6	$83.42	6.183%	$88.5779	$88.58	$88.60	$88.60
Purchase #7	$65.31	12.484%	$73.4633	$73.46	$73.45	$73.50
7 purchase totals =	$456.84		$505.8862	$505.90	$505.90	$505.90