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	$30.36	5.689%	$32.0872	$32.09	$32.10	$32.10
Purchase #2	$248.92	8.708%	$270.596	$270.60	$270.60	$270.60
Purchase #3	$151.88	6.626%	$161.9436	$161.94	$161.95	$161.90
Purchase #4	$98.38	13.322%	$111.4862	$111.49	$111.50	$111.50
Purchase #5	$74.55	11.654%	$83.2381	$83.24	$83.25	$83.20
Purchase #6	$216.84	13.210%	$245.4846	$245.48	$245.50	$245.50
Purchase #7	$93.82	11.463%	$104.5746	$104.57	$104.55	$104.60
7 purchase totals =	$914.75		$1,009.4103	$1,009.41	$1,009.45	$1,009.40