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	$104.71	10.272%	$115.4658	$115.47	$115.45	$115.50
Purchase #2	$182.74	7.590%	$196.61	$196.61	$196.60	$196.60
Purchase #3	$25.37	8.574%	$27.5452	$27.55	$27.55	$27.50
Purchase #4	$248.77	9.746%	$273.0151	$273.02	$273.00	$273.00
Purchase #5	$163.82	9.446%	$179.2944	$179.29	$179.30	$179.30
Purchase #6	$228.56	5.173%	$240.3834	$240.38	$240.40	$240.40
Purchase #7	$145.85	6.209%	$154.9058	$154.91	$154.90	$154.90
7 purchase totals =	$1,099.82		$1,187.2197	$1,187.23	$1,187.20	$1,187.20