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	$174.82	9.667%	$191.7198	$191.72	$191.70	$191.70
Purchase #2	$100.55	12.166%	$112.7829	$112.78	$112.80	$112.80
Purchase #3	$17.79	11.323%	$19.8044	$19.80	$19.80	$19.80
Purchase #4	$89.34	7.389%	$95.9413	$95.94	$95.95	$95.90
Purchase #5	$114.55	11.618%	$127.8584	$127.86	$127.85	$127.90
Purchase #6	$79.50	7.572%	$85.5197	$85.52	$85.50	$85.50
Purchase #7	$249.64	4.110%	$259.9002	$259.90	$259.90	$259.90
7 purchase totals =	$826.19		$893.5267	$893.52	$893.50	$893.50