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	$114.92	4.643%	$120.2557	$120.26	$120.25	$120.30
Purchase #2	$209.50	5.189%	$220.371	$220.37	$220.35	$220.40
Purchase #3	$246.54	4.211%	$256.9218	$256.92	$256.90	$256.90
Purchase #4	$55.75	9.196%	$60.8768	$60.88	$60.90	$60.90
Purchase #5	$116.74	5.717%	$123.414	$123.41	$123.40	$123.40
Purchase #6	$37.54	12.412%	$42.1995	$42.20	$42.20	$42.20
Purchase #7	$172.95	10.872%	$191.7531	$191.75	$191.75	$191.80
7 purchase totals =	$953.94		$1,015.7919	$1,015.79	$1,015.75	$1,015.90