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	$75.37	3.715%	$78.17	$78.17	$78.15	$78.20
Purchase #2	$228.94	5.198%	$240.8403	$240.84	$240.85	$240.80
Purchase #3	$154.31	11.196%	$171.5865	$171.59	$171.60	$171.60
Purchase #4	$41.52	3.607%	$43.0176	$43.02	$43.00	$43.00
Purchase #5	$40.70	5.694%	$43.0175	$43.02	$43.00	$43.00
Purchase #6	$84.41	12.732%	$95.1571	$95.16	$95.15	$95.20
Purchase #7	$133.38	7.666%	$143.6049	$143.60	$143.60	$143.60
7 purchase totals =	$758.63		$815.3939	$815.40	$815.35	$815.40