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	$164.46	4.124%	$171.2423	$171.24	$171.25	$171.20
Purchase #2	$65.49	3.164%	$67.5621	$67.56	$67.55	$67.60
Purchase #3	$166.39	6.643%	$177.4433	$177.44	$177.45	$177.40
Purchase #4	$125.30	12.102%	$140.4638	$140.46	$140.45	$140.50
Purchase #5	$29.32	11.807%	$32.7818	$32.78	$32.80	$32.80
Purchase #6	$30.33	8.313%	$32.8513	$32.85	$32.85	$32.90
Purchase #7	$45.73	13.815%	$52.0476	$52.05	$52.05	$52.00
7 purchase totals =	$627.02		$674.3922	$674.38	$674.40	$674.40