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	$249.77	9.435%	$273.3358	$273.34	$273.35	$273.30
Purchase #2	$80.76	12.221%	$90.6297	$90.63	$90.65	$90.60
Purchase #3	$88.94	7.505%	$95.6149	$95.61	$95.60	$95.60
Purchase #4	$12.88	12.362%	$14.4722	$14.47	$14.45	$14.50
Purchase #5	$203.54	11.795%	$227.5475	$227.55	$227.55	$227.50
Purchase #6	$41.34	7.227%	$44.3276	$44.33	$44.35	$44.30
Purchase #7	$51.69	10.279%	$57.0032	$57.00	$57.00	$57.00
7 purchase totals =	$728.92		$802.9309	$802.93	$802.95	$802.80