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	$85.46	5.740%	$90.3654	$90.37	$90.35	$90.40
Purchase #2	$85.36	9.399%	$93.383	$93.38	$93.40	$93.40
Purchase #3	$186.94	10.109%	$205.8378	$205.84	$205.85	$205.80
Purchase #4	$51.32	6.350%	$54.5788	$54.58	$54.60	$54.60
Purchase #5	$10.80	9.835%	$11.8622	$11.86	$11.85	$11.90
Purchase #6	$198.87	11.661%	$222.0602	$222.06	$222.05	$222.10
Purchase #7	$134.56	10.701%	$148.9593	$148.96	$148.95	$149.00
7 purchase totals =	$753.31		$827.0467	$827.05	$827.05	$827.20