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	$209.83	6.115%	$222.6611	$222.66	$222.65	$222.70
Purchase #2	$126.64	9.820%	$139.076	$139.08	$139.10	$139.10
Purchase #3	$82.66	7.339%	$88.7264	$88.73	$88.75	$88.70
Purchase #4	$59.43	11.599%	$66.3233	$66.32	$66.30	$66.30
Purchase #5	$84.49	6.591%	$90.0587	$90.06	$90.05	$90.10
Purchase #6	$87.40	12.427%	$98.2612	$98.26	$98.25	$98.30
Purchase #7	$80.48	9.412%	$88.0548	$88.05	$88.05	$88.10
7 purchase totals =	$730.93		$793.1615	$793.16	$793.15	$793.30