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	$125.56	6.382%	$133.5732	$133.57	$133.55	$133.60
Purchase #2	$191.84	6.590%	$204.4823	$204.48	$204.50	$204.50
Purchase #3	$210.44	8.541%	$228.4137	$228.41	$228.40	$228.40
Purchase #4	$143.89	5.152%	$151.3032	$151.30	$151.30	$151.30
Purchase #5	$232.78	5.633%	$245.8925	$245.89	$245.90	$245.90
Purchase #6	$38.60	5.397%	$40.6832	$40.68	$40.70	$40.70
Purchase #7	$65.31	10.383%	$72.0911	$72.09	$72.10	$72.10
7 purchase totals =	$1,008.42		$1,076.4392	$1,076.42	$1,076.45	$1,076.50