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	$199.79	4.714%	$209.2081	$209.21	$209.20	$209.20
Purchase #2	$131.38	7.223%	$140.8696	$140.87	$140.85	$140.90
Purchase #3	$127.50	11.333%	$141.9496	$141.95	$141.95	$141.90
Purchase #4	$106.30	13.646%	$120.8057	$120.81	$120.80	$120.80
Purchase #5	$118.53	11.654%	$132.3435	$132.34	$132.35	$132.30
Purchase #6	$127.50	12.295%	$143.1761	$143.18	$143.20	$143.20
Purchase #7	$235.90	11.488%	$263.0002	$263.00	$263.00	$263.00
7 purchase totals =	$1,046.90		$1,151.3528	$1,151.36	$1,151.35	$1,151.30