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	$59.70	12.661%	$67.2586	$67.26	$67.25	$67.30
Purchase #2	$18.38	10.433%	$20.2976	$20.30	$20.30	$20.30
Purchase #3	$159.38	13.315%	$180.6014	$180.60	$180.60	$180.60
Purchase #4	$139.56	4.402%	$145.7034	$145.70	$145.70	$145.70
Purchase #5	$82.35	11.213%	$91.5839	$91.58	$91.60	$91.60
Purchase #6	$132.71	3.525%	$137.388	$137.39	$137.40	$137.40
Purchase #7	$199.65	3.454%	$206.5459	$206.55	$206.55	$206.50
7 purchase totals =	$791.73		$849.3788	$849.38	$849.40	$849.40