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	$178.65	3.628%	$185.1314	$185.13	$185.15	$185.10
Purchase #2	$90.86	3.677%	$94.2009	$94.20	$94.20	$94.20
Purchase #3	$136.72	13.525%	$155.2114	$155.21	$155.20	$155.20
Purchase #4	$207.59	11.704%	$231.8863	$231.89	$231.90	$231.90
Purchase #5	$38.46	12.871%	$43.4102	$43.41	$43.40	$43.40
Purchase #6	$45.56	10.609%	$50.3935	$50.39	$50.40	$50.40
Purchase #7	$205.82	12.839%	$232.2452	$232.25	$232.25	$232.20
7 purchase totals =	$903.66		$992.4789	$992.48	$992.50	$992.40