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	$52.91	3.409%	$54.7137	$54.71	$54.70	$54.70
Purchase #2	$51.82	13.213%	$58.667	$58.67	$58.65	$58.70
Purchase #3	$139.64	7.591%	$150.2401	$150.24	$150.25	$150.20
Purchase #4	$54.42	12.688%	$61.3248	$61.32	$61.30	$61.30
Purchase #5	$100.90	3.645%	$104.5778	$104.58	$104.60	$104.60
Purchase #6	$33.56	3.462%	$34.7218	$34.72	$34.70	$34.70
Purchase #7	$187.38	13.331%	$212.3596	$212.36	$212.35	$212.40
7 purchase totals =	$620.63		$676.6048	$676.60	$676.55	$676.60