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	$131.76	3.376%	$136.2082	$136.21	$136.20	$136.20
Purchase #2	$96.69	13.668%	$109.9056	$109.91	$109.90	$109.90
Purchase #3	$9.55	3.237%	$9.8591	$9.86	$9.85	$9.90
Purchase #4	$87.53	3.108%	$90.2504	$90.25	$90.25	$90.30
Purchase #5	$126.45	13.488%	$143.5056	$143.51	$143.50	$143.50
Purchase #6	$55.54	7.471%	$59.6894	$59.69	$59.70	$59.70
Purchase #7	$234.67	12.867%	$264.865	$264.87	$264.85	$264.90
7 purchase totals =	$742.19		$814.2833	$814.30	$814.25	$814.40