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	$81.61	4.265%	$85.0907	$85.09	$85.10	$85.10
Purchase #2	$247.66	10.414%	$273.4513	$273.45	$273.45	$273.50
Purchase #3	$81.79	10.803%	$90.6258	$90.63	$90.65	$90.60
Purchase #4	$32.40	4.585%	$33.8855	$33.89	$33.90	$33.90
Purchase #5	$167.43	8.674%	$181.9529	$181.95	$181.95	$182.00
Purchase #6	$86.31	7.593%	$92.8635	$92.86	$92.85	$92.90
Purchase #7	$116.77	10.524%	$129.0589	$129.06	$129.05	$129.10
7 purchase totals =	$813.97		$886.9286	$886.93	$886.95	$887.10