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	$109.31	6.267%	$116.1605	$116.16	$116.15	$116.20
Purchase #2	$62.59	13.486%	$71.0309	$71.03	$71.05	$71.00
Purchase #3	$34.60	12.154%	$38.8053	$38.81	$38.80	$38.80
Purchase #4	$240.41	6.441%	$255.8948	$255.89	$255.90	$255.90
Purchase #5	$35.98	6.676%	$38.382	$38.38	$38.40	$38.40
Purchase #6	$209.56	5.634%	$221.3666	$221.37	$221.35	$221.40
Purchase #7	$29.96	10.277%	$33.039	$33.04	$33.05	$33.00
7 purchase totals =	$722.41		$774.6791	$774.68	$774.70	$774.70