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	$82.65	8.475%	$89.6546	$89.65	$89.65	$89.70
Purchase #2	$210.83	12.203%	$236.5576	$236.56	$236.55	$236.60
Purchase #3	$57.58	3.525%	$59.6097	$59.61	$59.60	$59.60
Purchase #4	$117.91	4.272%	$122.9471	$122.95	$122.95	$122.90
Purchase #5	$85.39	11.306%	$95.0442	$95.04	$95.05	$95.00
Purchase #6	$39.36	6.257%	$41.8228	$41.82	$41.80	$41.80
Purchase #7	$222.62	12.728%	$250.9551	$250.96	$250.95	$251.00
7 purchase totals =	$816.34		$896.5911	$896.59	$896.55	$896.60