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	$64.28	9.181%	$70.1815	$70.18	$70.20	$70.20
Purchase #2	$77.61	3.369%	$80.2247	$80.22	$80.20	$80.20
Purchase #3	$238.68	6.573%	$254.3684	$254.37	$254.35	$254.40
Purchase #4	$41.46	3.279%	$42.8195	$42.82	$42.80	$42.80
Purchase #5	$113.79	12.788%	$128.3415	$128.34	$128.35	$128.30
Purchase #6	$48.71	4.732%	$51.015	$51.02	$51.00	$51.00
Purchase #7	$118.91	10.870%	$131.8355	$131.84	$131.85	$131.80
7 purchase totals =	$703.44		$758.7861	$758.79	$758.75	$758.70