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	$29.69	6.528%	$31.6282	$31.63	$31.65	$31.60
Purchase #2	$44.89	12.206%	$50.3693	$50.37	$50.35	$50.40
Purchase #3	$249.48	9.809%	$273.9515	$273.95	$273.95	$274.00
Purchase #4	$166.92	8.532%	$181.1616	$181.16	$181.15	$181.20
Purchase #5	$133.30	4.510%	$139.3118	$139.31	$139.30	$139.30
Purchase #6	$214.60	4.197%	$223.6068	$223.61	$223.60	$223.60
Purchase #7	$137.48	13.310%	$155.7786	$155.78	$155.80	$155.80
7 purchase totals =	$976.36		$1,055.8078	$1,055.81	$1,055.80	$1,055.90