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	$121.50	12.346%	$136.5004	$136.50	$136.50	$136.50
Purchase #2	$143.61	4.598%	$150.2132	$150.21	$150.20	$150.20
Purchase #3	$110.93	13.692%	$126.1185	$126.12	$126.10	$126.10
Purchase #4	$52.32	13.660%	$59.4669	$59.47	$59.45	$59.50
Purchase #5	$203.29	9.447%	$222.4948	$222.49	$222.50	$222.50
Purchase #6	$241.38	9.269%	$263.7535	$263.75	$263.75	$263.80
Purchase #7	$171.70	10.303%	$189.3903	$189.39	$189.40	$189.40
7 purchase totals =	$1,044.73		$1,147.9376	$1,147.93	$1,147.90	$1,148.00