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	$21.27	12.288%	$23.8837	$23.88	$23.90	$23.90
Purchase #2	$18.76	9.374%	$20.5186	$20.52	$20.50	$20.50
Purchase #3	$94.66	11.425%	$105.4749	$105.47	$105.45	$105.50
Purchase #4	$37.87	4.241%	$39.4761	$39.48	$39.50	$39.50
Purchase #5	$72.68	11.196%	$80.8173	$80.82	$80.80	$80.80
Purchase #6	$243.36	11.609%	$271.6117	$271.61	$271.60	$271.60
Purchase #7	$96.71	12.258%	$108.5647	$108.56	$108.55	$108.60
7 purchase totals =	$585.31		$650.3470	$650.34	$650.30	$650.40