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	$51.89	5.499%	$54.7434	$54.74	$54.75	$54.70
Purchase #2	$37.44	12.140%	$41.9852	$41.99	$42.00	$42.00
Purchase #3	$35.75	10.401%	$39.4684	$39.47	$39.45	$39.50
Purchase #4	$48.97	5.695%	$51.7588	$51.76	$51.75	$51.80
Purchase #5	$204.43	11.795%	$228.5425	$228.54	$228.55	$228.50
Purchase #6	$54.46	9.384%	$59.5705	$59.57	$59.55	$59.60
Purchase #7	$44.64	11.274%	$49.6727	$49.67	$49.65	$49.70
7 purchase totals =	$477.58		$525.7415	$525.74	$525.70	$525.80