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	$199.91	13.102%	$226.1022	$226.10	$226.10	$226.10
Purchase #2	$18.62	10.736%	$20.619	$20.62	$20.60	$20.60
Purchase #3	$96.60	7.665%	$104.0044	$104.00	$104.00	$104.00
Purchase #4	$112.89	9.563%	$123.6857	$123.69	$123.70	$123.70
Purchase #5	$128.85	10.116%	$141.8845	$141.88	$141.90	$141.90
Purchase #6	$136.66	7.408%	$146.7838	$146.78	$146.80	$146.80
Purchase #7	$77.52	6.689%	$82.7053	$82.71	$82.70	$82.70
7 purchase totals =	$771.05		$845.7849	$845.78	$845.80	$845.80