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	$124.27	12.524%	$139.8336	$139.83	$139.85	$139.80
Purchase #2	$240.48	11.104%	$267.1829	$267.18	$267.20	$267.20
Purchase #3	$149.94	8.262%	$162.328	$162.33	$162.35	$162.30
Purchase #4	$98.78	13.318%	$111.9355	$111.94	$111.95	$111.90
Purchase #5	$109.81	12.321%	$123.3397	$123.34	$123.35	$123.30
Purchase #6	$87.61	13.641%	$99.5609	$99.56	$99.55	$99.60
Purchase #7	$233.75	8.569%	$253.78	$253.78	$253.80	$253.80
7 purchase totals =	$1,044.64		$1,157.9606	$1,157.96	$1,158.05	$1,157.90