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	$93.63	12.480%	$105.315	$105.32	$105.30	$105.30
Purchase #2	$78.33	6.219%	$83.2013	$83.20	$83.20	$83.20
Purchase #3	$186.56	10.860%	$206.8204	$206.82	$206.80	$206.80
Purchase #4	$239.63	6.848%	$256.0399	$256.04	$256.05	$256.00
Purchase #5	$132.39	6.738%	$141.3104	$141.31	$141.30	$141.30
Purchase #6	$51.65	4.325%	$53.8839	$53.88	$53.90	$53.90
Purchase #7	$140.92	10.726%	$156.0351	$156.04	$156.05	$156.00
7 purchase totals =	$923.11		$1,002.6060	$1,002.61	$1,002.60	$1,002.50