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	$9.25	6.633%	$9.8636	$9.86	$9.85	$9.90
Purchase #2	$246.35	12.803%	$277.8902	$277.89	$277.90	$277.90
Purchase #3	$116.87	5.361%	$123.1354	$123.14	$123.15	$123.10
Purchase #4	$143.55	11.115%	$159.5056	$159.51	$159.50	$159.50
Purchase #5	$184.82	4.206%	$192.5935	$192.59	$192.60	$192.60
Purchase #6	$250.59	5.844%	$265.2345	$265.23	$265.25	$265.20
Purchase #7	$143.34	13.597%	$162.8299	$162.83	$162.85	$162.80
7 purchase totals =	$1,094.77		$1,191.0527	$1,191.05	$1,191.10	$1,191.00