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	$34.37	7.435%	$36.9254	$36.93	$36.95	$36.90
Purchase #2	$223.25	7.217%	$239.362	$239.36	$239.35	$239.40
Purchase #3	$215.70	11.228%	$239.9188	$239.92	$239.90	$239.90
Purchase #4	$159.45	3.257%	$164.6433	$164.64	$164.65	$164.60
Purchase #5	$80.64	12.687%	$90.8708	$90.87	$90.85	$90.90
Purchase #6	$30.75	8.507%	$33.3659	$33.37	$33.35	$33.40
Purchase #7	$56.91	4.471%	$59.4544	$59.45	$59.45	$59.50
7 purchase totals =	$801.07		$864.5406	$864.54	$864.50	$864.60