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	$96.34	8.822%	$104.8391	$104.84	$104.85	$104.80
Purchase #2	$133.41	10.507%	$147.4274	$147.43	$147.45	$147.40
Purchase #3	$18.41	11.391%	$20.5071	$20.51	$20.50	$20.50
Purchase #4	$246.97	9.776%	$271.1138	$271.11	$271.10	$271.10
Purchase #5	$19.26	12.191%	$21.608	$21.61	$21.60	$21.60
Purchase #6	$105.98	10.314%	$116.9108	$116.91	$116.90	$116.90
Purchase #7	$136.93	4.575%	$143.1945	$143.19	$143.20	$143.20
7 purchase totals =	$757.30		$825.6007	$825.60	$825.60	$825.50