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	$159.60	4.526%	$166.8235	$166.82	$166.80	$166.80
Purchase #2	$10.82	9.114%	$11.8061	$11.81	$11.80	$11.80
Purchase #3	$75.31	4.818%	$78.9384	$78.94	$78.95	$78.90
Purchase #4	$135.43	11.107%	$150.4722	$150.47	$150.45	$150.50
Purchase #5	$78.29	9.172%	$85.4708	$85.47	$85.45	$85.50
Purchase #6	$111.36	13.312%	$126.1842	$126.18	$126.20	$126.20
Purchase #7	$218.78	9.581%	$239.7413	$239.74	$239.75	$239.70
7 purchase totals =	$789.59		$859.4365	$859.43	$859.40	$859.40