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	$62.43	7.147%	$66.8919	$66.89	$66.90	$66.90
Purchase #2	$111.42	6.365%	$118.5119	$118.51	$118.50	$118.50
Purchase #3	$96.34	13.641%	$109.4817	$109.48	$109.50	$109.50
Purchase #4	$76.85	13.831%	$87.4791	$87.48	$87.50	$87.50
Purchase #5	$152.35	4.361%	$158.994	$158.99	$159.00	$159.00
Purchase #6	$198.35	9.228%	$216.6537	$216.65	$216.65	$216.70
Purchase #7	$91.37	8.656%	$99.279	$99.28	$99.30	$99.30
7 purchase totals =	$789.11		$857.2913	$857.28	$857.35	$857.40