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	$20.76	4.721%	$21.7401	$21.74	$21.75	$21.70
Purchase #2	$59.48	3.713%	$61.6885	$61.69	$61.70	$61.70
Purchase #3	$95.86	9.395%	$104.866	$104.87	$104.85	$104.90
Purchase #4	$86.84	10.437%	$95.9035	$95.90	$95.90	$95.90
Purchase #5	$58.68	8.566%	$63.7065	$63.71	$63.70	$63.70
Purchase #6	$189.88	9.685%	$208.2699	$208.27	$208.25	$208.30
Purchase #7	$89.48	12.453%	$100.6229	$100.62	$100.60	$100.60
7 purchase totals =	$600.98		$656.7974	$656.80	$656.75	$656.80