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	$80.41	12.235%	$90.2482	$90.25	$90.25	$90.20
Purchase #2	$141.73	10.522%	$156.6428	$156.64	$156.65	$156.60
Purchase #3	$148.92	9.395%	$162.911	$162.91	$162.90	$162.90
Purchase #4	$209.32	6.641%	$223.2209	$223.22	$223.20	$223.20
Purchase #5	$98.71	4.296%	$102.9506	$102.95	$102.95	$103.00
Purchase #6	$54.81	3.874%	$56.9333	$56.93	$56.95	$56.90
Purchase #7	$37.82	3.318%	$39.0749	$39.07	$39.05	$39.10
7 purchase totals =	$771.72		$831.9817	$831.97	$831.95	$831.90