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	$53.26	12.452%	$59.8919	$59.89	$59.90	$59.90
Purchase #2	$29.85	5.437%	$31.4729	$31.47	$31.45	$31.50
Purchase #3	$22.99	11.851%	$25.7145	$25.71	$25.70	$25.70
Purchase #4	$35.56	6.531%	$37.8824	$37.88	$37.90	$37.90
Purchase #5	$114.51	8.185%	$123.8826	$123.88	$123.90	$123.90
Purchase #6	$143.51	8.542%	$155.7686	$155.77	$155.75	$155.80
Purchase #7	$111.84	3.338%	$115.5732	$115.57	$115.55	$115.60
7 purchase totals =	$511.52		$550.1861	$550.17	$550.15	$550.30