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	$128.39	13.395%	$145.5878	$145.59	$145.60	$145.60
Purchase #2	$250.68	5.107%	$263.4822	$263.48	$263.50	$263.50
Purchase #3	$130.82	3.309%	$135.1488	$135.15	$135.15	$135.10
Purchase #4	$119.30	11.814%	$133.3941	$133.39	$133.40	$133.40
Purchase #5	$228.81	11.686%	$255.5487	$255.55	$255.55	$255.50
Purchase #6	$18.88	10.729%	$20.9056	$20.91	$20.90	$20.90
Purchase #7	$64.89	9.724%	$71.1999	$71.20	$71.20	$71.20
7 purchase totals =	$941.77		$1,025.2671	$1,025.27	$1,025.30	$1,025.20