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	$203.95	8.313%	$220.9044	$220.90	$220.90	$220.90
Purchase #2	$172.93	13.443%	$196.177	$196.18	$196.20	$196.20
Purchase #3	$92.71	11.450%	$103.3253	$103.33	$103.35	$103.30
Purchase #4	$127.96	3.702%	$132.6971	$132.70	$132.70	$132.70
Purchase #5	$26.78	13.705%	$30.4502	$30.45	$30.45	$30.50
Purchase #6	$200.49	13.868%	$228.294	$228.29	$228.30	$228.30
Purchase #7	$211.50	9.454%	$231.4952	$231.50	$231.50	$231.50
7 purchase totals =	$1,036.32		$1,143.3432	$1,143.35	$1,143.40	$1,143.40