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	$66.79	6.755%	$71.3017	$71.30	$71.30	$71.30
Purchase #2	$74.57	10.799%	$82.6228	$82.62	$82.60	$82.60
Purchase #3	$177.80	6.140%	$188.7169	$188.72	$188.70	$188.70
Purchase #4	$230.27	10.381%	$254.1743	$254.17	$254.15	$254.20
Purchase #5	$168.71	10.770%	$186.8801	$186.88	$186.90	$186.90
Purchase #6	$232.73	12.675%	$262.2285	$262.23	$262.25	$262.20
Purchase #7	$67.96	5.534%	$71.7209	$71.72	$71.70	$71.70
7 purchase totals =	$1,018.83		$1,117.6452	$1,117.64	$1,117.60	$1,117.60