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	$83.26	7.265%	$89.3088	$89.31	$89.30	$89.30
Purchase #2	$39.65	13.187%	$44.8786	$44.88	$44.90	$44.90
Purchase #3	$168.55	13.137%	$190.6924	$190.69	$190.70	$190.70
Purchase #4	$194.97	8.230%	$211.016	$211.02	$211.00	$211.00
Purchase #5	$115.59	13.542%	$131.2432	$131.24	$131.25	$131.20
Purchase #6	$75.38	9.441%	$82.4966	$82.50	$82.50	$82.50
Purchase #7	$139.97	4.841%	$146.7459	$146.75	$146.75	$146.70
7 purchase totals =	$817.37		$896.3815	$896.39	$896.40	$896.30