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	$31.42	4.678%	$32.8898	$32.89	$32.90	$32.90
Purchase #2	$201.74	4.254%	$210.322	$210.32	$210.30	$210.30
Purchase #3	$241.86	11.777%	$270.3439	$270.34	$270.35	$270.30
Purchase #4	$111.54	4.362%	$116.4054	$116.41	$116.40	$116.40
Purchase #5	$74.33	12.354%	$83.5127	$83.51	$83.50	$83.50
Purchase #6	$132.32	8.652%	$143.7683	$143.77	$143.75	$143.80
Purchase #7	$111.51	13.628%	$126.7066	$126.71	$126.70	$126.70
7 purchase totals =	$904.72		$983.9487	$983.95	$983.90	$983.90