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	$100.26	5.555%	$105.8294	$105.83	$105.85	$105.80
Purchase #2	$122.35	9.364%	$133.8069	$133.81	$133.80	$133.80
Purchase #3	$150.39	4.165%	$156.6537	$156.65	$156.65	$156.70
Purchase #4	$80.26	11.775%	$89.7106	$89.71	$89.70	$89.70
Purchase #5	$131.91	8.649%	$143.3189	$143.32	$143.30	$143.30
Purchase #6	$182.89	11.220%	$203.4103	$203.41	$203.40	$203.40
Purchase #7	$79.38	7.456%	$85.2986	$85.30	$85.30	$85.30
7 purchase totals =	$847.44		$918.0284	$918.03	$918.00	$918.00