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	$89.99	10.610%	$99.5379	$99.54	$99.55	$99.50
Purchase #2	$148.87	11.102%	$165.3975	$165.40	$165.40	$165.40
Purchase #3	$178.30	8.510%	$193.4733	$193.47	$193.45	$193.50
Purchase #4	$216.82	13.872%	$246.8973	$246.90	$246.90	$246.90
Purchase #5	$72.63	8.182%	$78.5726	$78.57	$78.55	$78.60
Purchase #6	$196.91	3.144%	$203.1009	$203.10	$203.10	$203.10
Purchase #7	$44.96	10.443%	$49.6552	$49.66	$49.65	$49.70
7 purchase totals =	$948.48		$1,036.6347	$1,036.64	$1,036.60	$1,036.70