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	$141.82	9.522%	$155.3241	$155.32	$155.30	$155.30
Purchase #2	$182.98	12.855%	$206.5021	$206.50	$206.50	$206.50
Purchase #3	$75.51	6.249%	$80.2286	$80.23	$80.25	$80.20
Purchase #4	$49.81	9.743%	$54.663	$54.66	$54.65	$54.70
Purchase #5	$81.79	8.653%	$88.8673	$88.87	$88.85	$88.90
Purchase #6	$132.84	7.830%	$143.2414	$143.24	$143.25	$143.20
Purchase #7	$228.90	9.174%	$249.8993	$249.90	$249.90	$249.90
7 purchase totals =	$893.65		$978.7258	$978.72	$978.70	$978.70