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	$18.74	7.578%	$20.1601	$20.16	$20.15	$20.20
Purchase #2	$178.79	9.704%	$196.1398	$196.14	$196.15	$196.10
Purchase #3	$246.86	8.528%	$267.9122	$267.91	$267.90	$267.90
Purchase #4	$236.60	5.838%	$250.4127	$250.41	$250.40	$250.40
Purchase #5	$181.35	5.207%	$190.7929	$190.79	$190.80	$190.80
Purchase #6	$75.28	4.385%	$78.581	$78.58	$78.60	$78.60
Purchase #7	$99.87	6.642%	$106.5034	$106.50	$106.50	$106.50
7 purchase totals =	$1,037.49		$1,110.5021	$1,110.49	$1,110.50	$1,110.50