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	$108.94	13.335%	$123.4671	$123.47	$123.45	$123.50
Purchase #2	$185.50	7.349%	$199.1324	$199.13	$199.15	$199.10
Purchase #3	$21.95	11.424%	$24.4576	$24.46	$24.45	$24.50
Purchase #4	$84.94	7.175%	$91.0344	$91.03	$91.05	$91.00
Purchase #5	$130.55	11.872%	$146.0489	$146.05	$146.05	$146.00
Purchase #6	$31.60	13.416%	$35.8395	$35.84	$35.85	$35.80
Purchase #7	$216.54	13.554%	$245.8898	$245.89	$245.90	$245.90
7 purchase totals =	$780.02		$865.8697	$865.87	$865.90	$865.80