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	$89.98	10.448%	$99.3811	$99.38	$99.40	$99.40
Purchase #2	$45.37	10.586%	$50.1729	$50.17	$50.15	$50.20
Purchase #3	$172.80	12.813%	$194.9409	$194.94	$194.95	$194.90
Purchase #4	$25.78	4.788%	$27.0143	$27.01	$27.00	$27.00
Purchase #5	$57.51	8.102%	$62.1695	$62.17	$62.15	$62.20
Purchase #6	$245.52	12.848%	$277.0644	$277.06	$277.05	$277.10
Purchase #7	$128.63	9.544%	$140.9064	$140.91	$140.90	$140.90
7 purchase totals =	$765.59		$851.6495	$851.64	$851.60	$851.70