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	$65.61	8.724%	$71.3338	$71.33	$71.35	$71.30
Purchase #2	$200.86	10.454%	$221.8579	$221.86	$221.85	$221.90
Purchase #3	$30.28	9.796%	$33.2462	$33.25	$33.25	$33.20
Purchase #4	$38.74	9.275%	$42.3331	$42.33	$42.35	$42.30
Purchase #5	$211.51	9.685%	$231.9947	$231.99	$232.00	$232.00
Purchase #6	$157.57	8.696%	$171.2723	$171.27	$171.25	$171.30
Purchase #7	$202.57	7.845%	$218.4616	$218.46	$218.45	$218.50
7 purchase totals =	$907.14		$990.4996	$990.49	$990.50	$990.50