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	$28.49	10.280%	$31.4188	$31.42	$31.40	$31.40
Purchase #2	$238.53	4.552%	$249.3879	$249.39	$249.40	$249.40
Purchase #3	$182.27	3.613%	$188.8554	$188.86	$188.85	$188.90
Purchase #4	$110.77	4.401%	$115.645	$115.65	$115.65	$115.60
Purchase #5	$148.98	13.369%	$168.8971	$168.90	$168.90	$168.90
Purchase #6	$10.50	6.602%	$11.1932	$11.19	$11.20	$11.20
Purchase #7	$78.53	10.663%	$86.9037	$86.90	$86.90	$86.90
7 purchase totals =	$798.07		$852.3011	$852.31	$852.30	$852.30