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	$99.72	13.483%	$113.1652	$113.17	$113.15	$113.20
Purchase #2	$40.59	10.307%	$44.7736	$44.77	$44.75	$44.80
Purchase #3	$128.51	10.213%	$141.6347	$141.63	$141.65	$141.60
Purchase #4	$91.81	12.558%	$103.3395	$103.34	$103.35	$103.30
Purchase #5	$247.59	6.766%	$264.3419	$264.34	$264.35	$264.30
Purchase #6	$194.91	12.595%	$219.4589	$219.46	$219.45	$219.50
Purchase #7	$95.89	7.635%	$103.2112	$103.21	$103.20	$103.20
7 purchase totals =	$899.02		$989.9250	$989.92	$989.90	$989.90