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	$215.77	12.574%	$242.9009	$242.90	$242.90	$242.90
Purchase #2	$43.46	13.507%	$49.3301	$49.33	$49.35	$49.30
Purchase #3	$200.57	5.861%	$212.3254	$212.33	$212.35	$212.30
Purchase #4	$89.61	10.650%	$99.1535	$99.15	$99.15	$99.20
Purchase #5	$8.62	12.654%	$9.7108	$9.71	$9.70	$9.70
Purchase #6	$76.47	13.543%	$86.8263	$86.83	$86.85	$86.80
Purchase #7	$74.87	4.642%	$78.3455	$78.35	$78.35	$78.30
7 purchase totals =	$709.37		$778.5925	$778.60	$778.65	$778.50