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	$30.66	7.855%	$33.0683	$33.07	$33.05	$33.10
Purchase #2	$188.94	12.173%	$211.9397	$211.94	$211.95	$211.90
Purchase #3	$61.34	5.671%	$64.8186	$64.82	$64.80	$64.80
Purchase #4	$203.63	3.247%	$210.2419	$210.24	$210.25	$210.20
Purchase #5	$46.37	4.439%	$48.4284	$48.43	$48.45	$48.40
Purchase #6	$50.55	9.713%	$55.4599	$55.46	$55.45	$55.50
Purchase #7	$55.74	12.827%	$62.8898	$62.89	$62.90	$62.90
7 purchase totals =	$637.23		$686.8466	$686.85	$686.85	$686.80