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	$98.53	10.677%	$109.05	$109.05	$109.05	$109.10
Purchase #2	$231.64	10.399%	$255.7282	$255.73	$255.75	$255.70
Purchase #3	$164.28	4.690%	$171.9847	$171.98	$172.00	$172.00
Purchase #4	$239.71	10.432%	$264.7165	$264.72	$264.70	$264.70
Purchase #5	$164.37	3.265%	$169.7367	$169.74	$169.75	$169.70
Purchase #6	$219.34	4.123%	$228.3834	$228.38	$228.40	$228.40
Purchase #7	$169.94	11.671%	$189.7737	$189.77	$189.75	$189.80
7 purchase totals =	$1,287.81		$1,389.3732	$1,389.37	$1,389.40	$1,389.40