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	$81.63	3.206%	$84.2471	$84.25	$84.25	$84.20
Purchase #2	$161.51	10.345%	$178.2182	$178.22	$178.20	$178.20
Purchase #3	$97.67	11.686%	$109.0837	$109.08	$109.10	$109.10
Purchase #4	$165.54	10.532%	$182.9747	$182.97	$182.95	$183.00
Purchase #5	$90.80	11.139%	$100.9142	$100.91	$100.90	$100.90
Purchase #6	$44.81	7.863%	$48.3334	$48.33	$48.35	$48.30
Purchase #7	$80.27	11.841%	$89.7748	$89.77	$89.75	$89.80
7 purchase totals =	$722.23		$793.5461	$793.53	$793.50	$793.50