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	$131.32	9.453%	$143.7337	$143.73	$143.75	$143.70
Purchase #2	$222.39	6.686%	$237.259	$237.26	$237.25	$237.30
Purchase #3	$80.76	9.425%	$88.3716	$88.37	$88.35	$88.40
Purchase #4	$149.33	12.448%	$167.9186	$167.92	$167.90	$167.90
Purchase #5	$57.34	3.458%	$59.3228	$59.32	$59.30	$59.30
Purchase #6	$90.57	13.547%	$102.8395	$102.84	$102.85	$102.80
Purchase #7	$66.94	5.784%	$70.8118	$70.81	$70.80	$70.80
7 purchase totals =	$798.65		$870.2570	$870.25	$870.20	$870.20