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	$40.33	11.544%	$44.9857	$44.99	$45.00	$45.00
Purchase #2	$69.92	12.138%	$78.4069	$78.41	$78.40	$78.40
Purchase #3	$36.63	13.636%	$41.6249	$41.62	$41.60	$41.60
Purchase #4	$228.59	8.632%	$248.3219	$248.32	$248.30	$248.30
Purchase #5	$174.60	6.633%	$186.1812	$186.18	$186.20	$186.20
Purchase #6	$241.56	5.633%	$255.1671	$255.17	$255.15	$255.20
Purchase #7	$102.34	9.136%	$111.6898	$111.69	$111.70	$111.70
7 purchase totals =	$893.97		$966.3775	$966.38	$966.35	$966.40