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	$74.85	10.153%	$82.4495	$82.45	$82.45	$82.40
Purchase #2	$199.25	11.570%	$222.3032	$222.30	$222.30	$222.30
Purchase #3	$190.57	4.590%	$199.3172	$199.32	$199.30	$199.30
Purchase #4	$57.87	7.495%	$62.2074	$62.21	$62.20	$62.20
Purchase #5	$85.58	9.710%	$93.8898	$93.89	$93.90	$93.90
Purchase #6	$230.89	12.567%	$259.9059	$259.91	$259.90	$259.90
Purchase #7	$17.68	6.648%	$18.8554	$18.86	$18.85	$18.90
7 purchase totals =	$856.69		$938.9284	$938.94	$938.90	$938.90