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	$200.94	3.153%	$207.2756	$207.28	$207.30	$207.30
Purchase #2	$75.71	3.809%	$78.5938	$78.59	$78.60	$78.60
Purchase #3	$78.66	12.318%	$88.3493	$88.35	$88.35	$88.30
Purchase #4	$207.41	10.588%	$229.3706	$229.37	$229.35	$229.40
Purchase #5	$125.40	7.237%	$134.4752	$134.48	$134.50	$134.50
Purchase #6	$154.73	3.779%	$160.5772	$160.58	$160.60	$160.60
Purchase #7	$87.86	3.459%	$90.8991	$90.90	$90.90	$90.90
7 purchase totals =	$930.71		$989.5408	$989.55	$989.60	$989.60