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	$70.57	11.852%	$78.934	$78.93	$78.95	$78.90
Purchase #2	$200.83	13.287%	$227.5143	$227.51	$227.50	$227.50
Purchase #3	$63.86	5.688%	$67.4924	$67.49	$67.50	$67.50
Purchase #4	$12.88	12.864%	$14.5369	$14.54	$14.55	$14.50
Purchase #5	$176.49	13.115%	$199.6367	$199.64	$199.65	$199.60
Purchase #6	$79.31	13.161%	$89.748	$89.75	$89.75	$89.70
Purchase #7	$106.65	12.753%	$120.2511	$120.25	$120.25	$120.30
7 purchase totals =	$710.59		$798.1134	$798.11	$798.15	$798.00