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	$74.62	9.191%	$81.4783	$81.48	$81.50	$81.50
Purchase #2	$28.47	11.724%	$31.8078	$31.81	$31.80	$31.80
Purchase #3	$105.82	10.260%	$116.6771	$116.68	$116.70	$116.70
Purchase #4	$249.27	9.780%	$273.6486	$273.65	$273.65	$273.60
Purchase #5	$222.83	13.867%	$253.7298	$253.73	$253.75	$253.70
Purchase #6	$178.96	9.259%	$195.5299	$195.53	$195.55	$195.50
Purchase #7	$171.85	10.139%	$189.2739	$189.27	$189.25	$189.30
7 purchase totals =	$1,031.82		$1,142.1454	$1,142.15	$1,142.20	$1,142.10