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	$59.85	7.547%	$64.3669	$64.37	$64.35	$64.40
Purchase #2	$76.48	3.163%	$78.8991	$78.90	$78.90	$78.90
Purchase #3	$39.49	5.808%	$41.7836	$41.78	$41.80	$41.80
Purchase #4	$92.77	7.404%	$99.6387	$99.64	$99.65	$99.60
Purchase #5	$159.48	12.720%	$179.7659	$179.77	$179.75	$179.80
Purchase #6	$70.67	10.759%	$78.2734	$78.27	$78.25	$78.30
Purchase #7	$46.31	3.782%	$48.0614	$48.06	$48.05	$48.10
7 purchase totals =	$545.05		$590.7890	$590.79	$590.75	$590.90