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	$32.67	6.333%	$34.739	$34.74	$34.75	$34.70
Purchase #2	$93.58	13.477%	$106.1918	$106.19	$106.20	$106.20
Purchase #3	$190.33	13.177%	$215.4098	$215.41	$215.40	$215.40
Purchase #4	$53.96	9.458%	$59.0635	$59.06	$59.05	$59.10
Purchase #5	$74.96	5.285%	$78.9216	$78.92	$78.90	$78.90
Purchase #6	$108.33	11.543%	$120.8345	$120.83	$120.85	$120.80
Purchase #7	$49.97	12.799%	$56.3657	$56.37	$56.35	$56.40
7 purchase totals =	$603.80		$671.5259	$671.52	$671.50	$671.50