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	$80.54	6.577%	$85.8371	$85.84	$85.85	$85.80
Purchase #2	$202.36	10.285%	$223.1727	$223.17	$223.15	$223.20
Purchase #3	$42.49	10.144%	$46.8002	$46.80	$46.80	$46.80
Purchase #4	$94.76	4.390%	$98.92	$98.92	$98.90	$98.90
Purchase #5	$7.98	4.366%	$8.3284	$8.33	$8.35	$8.30
Purchase #6	$134.36	4.385%	$140.2517	$140.25	$140.25	$140.30
Purchase #7	$43.72	8.846%	$47.5875	$47.59	$47.60	$47.60
7 purchase totals =	$606.21		$650.8976	$650.90	$650.90	$650.90