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	$184.84	8.390%	$200.3481	$200.35	$200.35	$200.30
Purchase #2	$75.64	9.147%	$82.5588	$82.56	$82.55	$82.60
Purchase #3	$174.61	12.500%	$196.4363	$196.44	$196.45	$196.40
Purchase #4	$41.75	5.354%	$43.9853	$43.99	$44.00	$44.00
Purchase #5	$105.28	13.774%	$119.7813	$119.78	$119.80	$119.80
Purchase #6	$250.36	5.695%	$264.618	$264.62	$264.60	$264.60
Purchase #7	$55.39	12.583%	$62.3597	$62.36	$62.35	$62.40
7 purchase totals =	$887.87		$970.0875	$970.10	$970.10	$970.10