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	$130.93	9.663%	$143.5818	$143.58	$143.60	$143.60
Purchase #2	$136.59	11.345%	$152.0861	$152.09	$152.10	$152.10
Purchase #3	$250.25	10.778%	$277.2219	$277.22	$277.20	$277.20
Purchase #4	$37.54	7.130%	$40.2166	$40.22	$40.20	$40.20
Purchase #5	$91.45	3.727%	$94.8583	$94.86	$94.85	$94.90
Purchase #6	$193.41	11.837%	$216.3039	$216.30	$216.30	$216.30
Purchase #7	$99.81	12.836%	$112.6216	$112.62	$112.60	$112.60
7 purchase totals =	$939.98		$1,036.8902	$1,036.89	$1,036.85	$1,036.90