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	$152.52	8.717%	$165.8152	$165.82	$165.80	$165.80
Purchase #2	$103.62	11.245%	$115.2721	$115.27	$115.25	$115.30
Purchase #3	$239.86	4.148%	$249.8094	$249.81	$249.80	$249.80
Purchase #4	$172.49	13.365%	$195.5433	$195.54	$195.55	$195.50
Purchase #5	$135.55	6.573%	$144.4597	$144.46	$144.45	$144.50
Purchase #6	$167.39	7.748%	$180.3594	$180.36	$180.35	$180.40
Purchase #7	$103.40	7.690%	$111.3515	$111.35	$111.35	$111.40
7 purchase totals =	$1,074.83		$1,162.6106	$1,162.61	$1,162.55	$1,162.70