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	$158.54	4.550%	$165.7536	$165.75	$165.75	$165.80
Purchase #2	$115.53	3.600%	$119.6891	$119.69	$119.70	$119.70
Purchase #3	$224.90	6.510%	$239.541	$239.54	$239.55	$239.50
Purchase #4	$18.66	10.325%	$20.5866	$20.59	$20.60	$20.60
Purchase #5	$216.45	13.207%	$245.0366	$245.04	$245.05	$245.00
Purchase #6	$55.45	4.388%	$57.8831	$57.88	$57.90	$57.90
Purchase #7	$67.63	7.716%	$72.8483	$72.85	$72.85	$72.80
7 purchase totals =	$857.16		$921.3383	$921.34	$921.40	$921.30