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	$124.61	3.825%	$129.3763	$129.38	$129.40	$129.40
Purchase #2	$94.76	4.632%	$99.1493	$99.15	$99.15	$99.10
Purchase #3	$248.89	8.722%	$270.5982	$270.60	$270.60	$270.60
Purchase #4	$38.84	12.735%	$43.7863	$43.79	$43.80	$43.80
Purchase #5	$160.63	11.700%	$179.4237	$179.42	$179.40	$179.40
Purchase #6	$74.45	5.635%	$78.6453	$78.65	$78.65	$78.60
Purchase #7	$80.25	4.506%	$83.8661	$83.87	$83.85	$83.90
7 purchase totals =	$822.43		$884.8452	$884.86	$884.85	$884.80