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	$94.49	6.739%	$100.8577	$100.86	$100.85	$100.90
Purchase #2	$32.40	13.578%	$36.7993	$36.80	$36.80	$36.80
Purchase #3	$236.44	8.148%	$255.7051	$255.71	$255.70	$255.70
Purchase #4	$202.62	6.534%	$215.8592	$215.86	$215.85	$215.90
Purchase #5	$40.28	5.672%	$42.5647	$42.56	$42.55	$42.60
Purchase #6	$244.55	10.337%	$269.8291	$269.83	$269.85	$269.80
Purchase #7	$180.40	11.647%	$201.4112	$201.41	$201.40	$201.40
7 purchase totals =	$1,031.18		$1,123.0263	$1,123.03	$1,123.00	$1,123.10