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	$129.49	6.445%	$137.8356	$137.84	$137.85	$137.80
Purchase #2	$75.41	13.259%	$85.4086	$85.41	$85.40	$85.40
Purchase #3	$139.35	13.172%	$157.7052	$157.71	$157.70	$157.70
Purchase #4	$152.40	8.320%	$165.0797	$165.08	$165.10	$165.10
Purchase #5	$220.86	8.789%	$240.2714	$240.27	$240.25	$240.30
Purchase #6	$102.86	9.191%	$112.3139	$112.31	$112.30	$112.30
Purchase #7	$184.34	6.668%	$196.6318	$196.63	$196.65	$196.60
7 purchase totals =	$1,004.71		$1,095.2462	$1,095.25	$1,095.25	$1,095.20