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	$186.77	13.787%	$212.52	$212.52	$212.50	$212.50
Purchase #2	$215.36	8.841%	$234.4	$234.40	$234.40	$234.40
Purchase #3	$112.85	10.589%	$124.7997	$124.80	$124.80	$124.80
Purchase #4	$238.66	12.570%	$268.6596	$268.66	$268.65	$268.70
Purchase #5	$82.58	9.621%	$90.525	$90.53	$90.55	$90.50
Purchase #6	$215.76	3.302%	$222.8844	$222.88	$222.90	$222.90
Purchase #7	$189.41	7.548%	$203.7067	$203.71	$203.70	$203.70
7 purchase totals =	$1,241.39		$1,357.4954	$1,357.50	$1,357.50	$1,357.50