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	$39.55	13.557%	$44.9118	$44.91	$44.90	$44.90
Purchase #2	$86.40	11.748%	$96.5503	$96.55	$96.55	$96.60
Purchase #3	$77.69	10.241%	$85.6462	$85.65	$85.65	$85.60
Purchase #4	$136.96	5.307%	$144.2285	$144.23	$144.25	$144.20
Purchase #5	$148.27	5.835%	$156.9216	$156.92	$156.90	$156.90
Purchase #6	$54.68	12.859%	$61.7113	$61.71	$61.70	$61.70
Purchase #7	$238.61	12.578%	$268.6224	$268.62	$268.60	$268.60
7 purchase totals =	$782.16		$858.5921	$858.59	$858.55	$858.50