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	$35.48	6.830%	$37.9033	$37.90	$37.90	$37.90
Purchase #2	$212.48	12.457%	$238.9486	$238.95	$238.95	$238.90
Purchase #3	$115.79	12.556%	$130.3286	$130.33	$130.35	$130.30
Purchase #4	$40.61	7.309%	$43.5782	$43.58	$43.60	$43.60
Purchase #5	$133.66	5.856%	$141.4871	$141.49	$141.50	$141.50
Purchase #6	$142.56	8.142%	$154.1672	$154.17	$154.15	$154.20
Purchase #7	$97.56	7.809%	$105.1785	$105.18	$105.20	$105.20
7 purchase totals =	$778.14		$851.5915	$851.60	$851.65	$851.60