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	$143.40	5.794%	$151.7086	$151.71	$151.70	$151.70
Purchase #2	$34.48	8.828%	$37.5239	$37.52	$37.50	$37.50
Purchase #3	$12.39	4.129%	$12.9016	$12.90	$12.90	$12.90
Purchase #4	$200.76	12.527%	$225.9092	$225.91	$225.90	$225.90
Purchase #5	$135.53	5.582%	$143.0953	$143.10	$143.10	$143.10
Purchase #6	$196.81	12.820%	$222.041	$222.04	$222.05	$222.00
Purchase #7	$129.33	4.177%	$134.7321	$134.73	$134.75	$134.70
7 purchase totals =	$852.70		$927.9117	$927.91	$927.90	$927.80