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	$77.46	12.187%	$86.9001	$86.90	$86.90	$86.90
Purchase #2	$138.98	12.809%	$156.7819	$156.78	$156.80	$156.80
Purchase #3	$55.98	9.541%	$61.3211	$61.32	$61.30	$61.30
Purchase #4	$166.80	11.300%	$185.6484	$185.65	$185.65	$185.60
Purchase #5	$235.54	9.225%	$257.2686	$257.27	$257.25	$257.30
Purchase #6	$53.52	6.262%	$56.8714	$56.87	$56.85	$56.90
Purchase #7	$250.54	7.398%	$269.0749	$269.07	$269.05	$269.10
7 purchase totals =	$978.82		$1,073.8664	$1,073.86	$1,073.80	$1,073.90