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	$189.96	4.785%	$199.0496	$199.05	$199.05	$199.00
Purchase #2	$70.66	12.642%	$79.5928	$79.59	$79.60	$79.60
Purchase #3	$167.92	13.380%	$190.3877	$190.39	$190.40	$190.40
Purchase #4	$181.80	13.333%	$206.0394	$206.04	$206.05	$206.00
Purchase #5	$118.98	7.170%	$127.5109	$127.51	$127.50	$127.50
Purchase #6	$208.59	11.800%	$233.2036	$233.20	$233.20	$233.20
Purchase #7	$242.97	12.650%	$273.7057	$273.71	$273.70	$273.70
7 purchase totals =	$1,180.88		$1,309.4897	$1,309.49	$1,309.50	$1,309.40