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	$233.69	6.505%	$248.8915	$248.89	$248.90	$248.90
Purchase #2	$210.72	3.821%	$218.7716	$218.77	$218.75	$218.80
Purchase #3	$122.79	13.570%	$139.4526	$139.45	$139.45	$139.50
Purchase #4	$234.94	12.559%	$264.4461	$264.45	$264.45	$264.40
Purchase #5	$88.93	11.685%	$99.3215	$99.32	$99.30	$99.30
Purchase #6	$201.74	10.181%	$222.2791	$222.28	$222.30	$222.30
Purchase #7	$240.51	9.248%	$262.7524	$262.75	$262.75	$262.80
7 purchase totals =	$1,333.32		$1,455.9148	$1,455.91	$1,455.90	$1,456.00