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	$110.46	11.506%	$123.1695	$123.17	$123.15	$123.20
Purchase #2	$72.34	3.808%	$75.0947	$75.09	$75.10	$75.10
Purchase #3	$136.92	8.552%	$148.6294	$148.63	$148.65	$148.60
Purchase #4	$171.83	10.858%	$190.4873	$190.49	$190.50	$190.50
Purchase #5	$42.37	6.567%	$45.1524	$45.15	$45.15	$45.20
Purchase #6	$178.51	12.418%	$200.6774	$200.68	$200.70	$200.70
Purchase #7	$189.33	4.488%	$197.8271	$197.83	$197.85	$197.80
7 purchase totals =	$901.76		$981.0378	$981.04	$981.10	$981.10