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	$53.96	4.119%	$56.1826	$56.18	$56.20	$56.20
Purchase #2	$72.94	4.814%	$76.4513	$76.45	$76.45	$76.50
Purchase #3	$151.69	11.162%	$168.6216	$168.62	$168.60	$168.60
Purchase #4	$99.81	8.539%	$108.3328	$108.33	$108.35	$108.30
Purchase #5	$56.78	13.438%	$64.4101	$64.41	$64.40	$64.40
Purchase #6	$202.43	6.333%	$215.2499	$215.25	$215.25	$215.20
Purchase #7	$134.76	8.510%	$146.2281	$146.23	$146.25	$146.20
7 purchase totals =	$772.37		$835.4764	$835.47	$835.50	$835.40