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	$72.32	9.167%	$78.9496	$78.95	$78.95	$78.90
Purchase #2	$61.88	13.744%	$70.3848	$70.38	$70.40	$70.40
Purchase #3	$162.75	5.794%	$172.1797	$172.18	$172.20	$172.20
Purchase #4	$41.72	12.672%	$47.0068	$47.01	$47.00	$47.00
Purchase #5	$154.41	12.215%	$173.2712	$173.27	$173.25	$173.30
Purchase #6	$85.73	12.211%	$96.1985	$96.20	$96.20	$96.20
Purchase #7	$175.81	8.109%	$190.0664	$190.07	$190.05	$190.10
7 purchase totals =	$754.62		$828.0570	$828.06	$828.05	$828.10