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	$108.91	12.378%	$122.3909	$122.39	$122.40	$122.40
Purchase #2	$156.70	9.403%	$171.4345	$171.43	$171.45	$171.40
Purchase #3	$22.88	12.380%	$25.7125	$25.71	$25.70	$25.70
Purchase #4	$165.98	8.132%	$179.4775	$179.48	$179.50	$179.50
Purchase #5	$235.30	3.408%	$243.319	$243.32	$243.30	$243.30
Purchase #6	$156.34	13.193%	$176.9659	$176.97	$176.95	$177.00
Purchase #7	$53.71	9.862%	$59.0069	$59.01	$59.00	$59.00
7 purchase totals =	$899.82		$978.3072	$978.31	$978.30	$978.30