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	$70.31	11.534%	$78.4196	$78.42	$78.40	$78.40
Purchase #2	$203.50	13.403%	$230.7751	$230.78	$230.80	$230.80
Purchase #3	$182.70	5.798%	$193.2929	$193.29	$193.30	$193.30
Purchase #4	$18.27	12.253%	$20.5086	$20.51	$20.50	$20.50
Purchase #5	$116.30	7.514%	$125.0388	$125.04	$125.05	$125.00
Purchase #6	$184.76	6.591%	$196.9375	$196.94	$196.95	$196.90
Purchase #7	$80.93	13.496%	$91.8523	$91.85	$91.85	$91.90
7 purchase totals =	$856.77		$936.8248	$936.83	$936.85	$936.80