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	$109.90	7.702%	$118.3645	$118.36	$118.35	$118.40
Purchase #2	$91.93	9.789%	$100.929	$100.93	$100.95	$100.90
Purchase #3	$82.84	6.783%	$88.459	$88.46	$88.45	$88.50
Purchase #4	$51.46	8.214%	$55.6869	$55.69	$55.70	$55.70
Purchase #5	$182.47	3.849%	$189.4933	$189.49	$189.50	$189.50
Purchase #6	$70.30	12.275%	$78.9293	$78.93	$78.95	$78.90
Purchase #7	$119.45	9.696%	$131.0319	$131.03	$131.05	$131.00
7 purchase totals =	$708.35		$762.8939	$762.89	$762.95	$762.90