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	$211.70	7.436%	$227.442	$227.44	$227.45	$227.40
Purchase #2	$243.42	12.306%	$273.3753	$273.38	$273.40	$273.40
Purchase #3	$91.31	4.300%	$95.2363	$95.24	$95.25	$95.20
Purchase #4	$104.33	11.232%	$116.0483	$116.05	$116.05	$116.00
Purchase #5	$106.70	4.461%	$111.4599	$111.46	$111.45	$111.50
Purchase #6	$73.37	8.420%	$79.5478	$79.55	$79.55	$79.50
Purchase #7	$125.49	9.605%	$137.5433	$137.54	$137.55	$137.50
7 purchase totals =	$956.32		$1,040.6529	$1,040.66	$1,040.70	$1,040.50