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	$80.49	5.779%	$85.1415	$85.14	$85.15	$85.10
Purchase #2	$75.55	4.179%	$78.7072	$78.71	$78.70	$78.70
Purchase #3	$37.98	3.654%	$39.3678	$39.37	$39.35	$39.40
Purchase #4	$118.44	8.747%	$128.7999	$128.80	$128.80	$128.80
Purchase #5	$174.26	3.586%	$180.509	$180.51	$180.50	$180.50
Purchase #6	$250.40	13.687%	$284.6722	$284.67	$284.65	$284.70
Purchase #7	$240.40	13.674%	$273.2723	$273.27	$273.25	$273.30
7 purchase totals =	$977.52		$1,070.4699	$1,070.47	$1,070.40	$1,070.50