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	$84.51	6.692%	$90.1654	$90.17	$90.15	$90.20
Purchase #2	$142.50	8.819%	$155.0671	$155.07	$155.05	$155.10
Purchase #3	$90.41	11.132%	$100.4744	$100.47	$100.45	$100.50
Purchase #4	$82.68	6.671%	$88.1956	$88.20	$88.20	$88.20
Purchase #5	$52.79	12.832%	$59.564	$59.56	$59.55	$59.60
Purchase #6	$75.81	4.609%	$79.3041	$79.30	$79.30	$79.30
Purchase #7	$109.47	3.411%	$113.204	$113.20	$113.20	$113.20
7 purchase totals =	$638.17		$685.9746	$685.97	$685.90	$686.10