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	$37.58	12.269%	$42.1907	$42.19	$42.20	$42.20
Purchase #2	$211.83	7.388%	$227.48	$227.48	$227.50	$227.50
Purchase #3	$233.43	5.501%	$246.271	$246.27	$246.25	$246.30
Purchase #4	$96.96	12.419%	$109.0015	$109.00	$109.00	$109.00
Purchase #5	$139.50	13.620%	$158.4999	$158.50	$158.50	$158.50
Purchase #6	$78.48	6.855%	$83.8598	$83.86	$83.85	$83.90
Purchase #7	$30.92	3.443%	$31.9846	$31.98	$32.00	$32.00
7 purchase totals =	$828.70		$899.2875	$899.28	$899.30	$899.40