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	$168.75	12.314%	$189.5299	$189.53	$189.55	$189.50
Purchase #2	$50.81	10.609%	$56.2004	$56.20	$56.20	$56.20
Purchase #3	$194.55	9.534%	$213.0984	$213.10	$213.10	$213.10
Purchase #4	$85.92	3.368%	$88.8138	$88.81	$88.80	$88.80
Purchase #5	$16.86	10.256%	$18.5892	$18.59	$18.60	$18.60
Purchase #6	$121.62	7.626%	$130.8947	$130.89	$130.90	$130.90
Purchase #7	$66.88	3.820%	$69.4348	$69.43	$69.45	$69.40
7 purchase totals =	$705.39		$766.5612	$766.55	$766.60	$766.50