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	$239.78	13.127%	$271.2559	$271.26	$271.25	$271.30
Purchase #2	$221.72	11.593%	$247.424	$247.42	$247.40	$247.40
Purchase #3	$69.63	9.700%	$76.3841	$76.38	$76.40	$76.40
Purchase #4	$95.35	3.103%	$98.3087	$98.31	$98.30	$98.30
Purchase #5	$94.49	11.588%	$105.4395	$105.44	$105.45	$105.40
Purchase #6	$211.83	6.419%	$225.4274	$225.43	$225.45	$225.40
Purchase #7	$249.99	10.646%	$276.6039	$276.60	$276.60	$276.60
7 purchase totals =	$1,182.79		$1,300.8435	$1,300.84	$1,300.85	$1,300.80