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	$48.42	11.118%	$53.8033	$53.80	$53.80	$53.80
Purchase #2	$38.33	10.710%	$42.4351	$42.44	$42.45	$42.40
Purchase #3	$91.31	7.452%	$98.1144	$98.11	$98.10	$98.10
Purchase #4	$157.67	9.676%	$172.9261	$172.93	$172.95	$172.90
Purchase #5	$63.93	13.737%	$72.7121	$72.71	$72.70	$72.70
Purchase #6	$68.64	5.150%	$72.175	$72.18	$72.20	$72.20
Purchase #7	$78.80	8.109%	$85.1899	$85.19	$85.20	$85.20
7 purchase totals =	$547.10		$597.3559	$597.36	$597.40	$597.30