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	$139.72	6.241%	$148.4399	$148.44	$148.45	$148.40
Purchase #2	$58.74	3.855%	$61.0044	$61.00	$61.00	$61.00
Purchase #3	$93.37	12.414%	$104.961	$104.96	$104.95	$105.00
Purchase #4	$73.74	3.450%	$76.284	$76.28	$76.30	$76.30
Purchase #5	$58.59	8.752%	$63.7178	$63.72	$63.70	$63.70
Purchase #6	$90.72	11.192%	$100.8734	$100.87	$100.85	$100.90
Purchase #7	$108.76	5.164%	$114.3764	$114.38	$114.40	$114.40
7 purchase totals =	$623.64		$669.6569	$669.65	$669.65	$669.70