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	$249.30	4.502%	$260.5235	$260.52	$260.50	$260.50
Purchase #2	$95.33	4.357%	$99.4835	$99.48	$99.50	$99.50
Purchase #3	$33.85	13.523%	$38.4275	$38.43	$38.45	$38.40
Purchase #4	$152.72	4.830%	$160.0964	$160.10	$160.10	$160.10
Purchase #5	$94.72	10.294%	$104.4705	$104.47	$104.45	$104.50
Purchase #6	$39.59	11.235%	$44.0379	$44.04	$44.05	$44.00
Purchase #7	$100.53	13.593%	$114.195	$114.20	$114.20	$114.20
7 purchase totals =	$766.04		$821.2343	$821.24	$821.25	$821.20