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	$232.27	4.277%	$242.2042	$242.20	$242.20	$242.20
Purchase #2	$82.27	7.539%	$88.4723	$88.47	$88.45	$88.50
Purchase #3	$203.56	9.107%	$222.0982	$222.10	$222.10	$222.10
Purchase #4	$171.97	9.727%	$188.6975	$188.70	$188.70	$188.70
Purchase #5	$198.78	12.478%	$223.5838	$223.58	$223.60	$223.60
Purchase #6	$53.25	3.576%	$55.1542	$55.15	$55.15	$55.20
Purchase #7	$33.61	10.137%	$37.017	$37.02	$37.00	$37.00
7 purchase totals =	$975.71		$1,057.2272	$1,057.22	$1,057.20	$1,057.30