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	$82.89	3.122%	$85.4778	$85.48	$85.50	$85.50
Purchase #2	$101.52	11.734%	$113.4324	$113.43	$113.45	$113.40
Purchase #3	$78.91	5.174%	$82.9928	$82.99	$83.00	$83.00
Purchase #4	$92.97	13.771%	$105.7729	$105.77	$105.75	$105.80
Purchase #5	$178.55	12.342%	$200.5866	$200.59	$200.60	$200.60
Purchase #6	$28.44	6.146%	$30.1879	$30.19	$30.20	$30.20
Purchase #7	$221.29	3.801%	$229.7012	$229.70	$229.70	$229.70
7 purchase totals =	$784.57		$848.1516	$848.15	$848.20	$848.20