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	$182.83	3.644%	$189.4923	$189.49	$189.50	$189.50
Purchase #2	$185.38	12.663%	$208.8547	$208.85	$208.85	$208.90
Purchase #3	$201.32	7.671%	$216.7633	$216.76	$216.75	$216.80
Purchase #4	$213.25	4.710%	$223.2941	$223.29	$223.30	$223.30
Purchase #5	$231.79	7.793%	$249.8534	$249.85	$249.85	$249.90
Purchase #6	$176.92	10.158%	$194.8915	$194.89	$194.90	$194.90
Purchase #7	$7.60	4.540%	$7.945	$7.95	$7.95	$7.90
7 purchase totals =	$1,199.09		$1,291.0943	$1,291.08	$1,291.10	$1,291.20