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	$51.72	7.391%	$55.5426	$55.54	$55.55	$55.50
Purchase #2	$184.60	4.815%	$193.4885	$193.49	$193.50	$193.50
Purchase #3	$45.89	4.215%	$47.8243	$47.82	$47.80	$47.80
Purchase #4	$53.76	13.189%	$60.8504	$60.85	$60.85	$60.90
Purchase #5	$14.92	11.760%	$16.6746	$16.67	$16.65	$16.70
Purchase #6	$27.27	4.512%	$28.5004	$28.50	$28.50	$28.50
Purchase #7	$91.81	4.330%	$95.7854	$95.79	$95.80	$95.80
7 purchase totals =	$469.97		$498.6662	$498.66	$498.65	$498.70