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	$121.84	3.819%	$126.4931	$126.49	$126.50	$126.50
Purchase #2	$182.31	7.838%	$196.5995	$196.60	$196.60	$196.60
Purchase #3	$125.54	4.241%	$130.8642	$130.86	$130.85	$130.90
Purchase #4	$134.61	13.462%	$152.7312	$152.73	$152.75	$152.70
Purchase #5	$30.72	12.113%	$34.4411	$34.44	$34.45	$34.40
Purchase #6	$65.67	9.199%	$71.711	$71.71	$71.70	$71.70
Purchase #7	$188.44	10.709%	$208.62	$208.62	$208.60	$208.60
7 purchase totals =	$849.13		$921.4601	$921.45	$921.45	$921.40