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	$140.73	6.799%	$150.2982	$150.30	$150.30	$150.30
Purchase #2	$245.91	7.766%	$265.0074	$265.01	$265.00	$265.00
Purchase #3	$214.66	11.150%	$238.5946	$238.59	$238.60	$238.60
Purchase #4	$140.73	13.765%	$160.1015	$160.10	$160.10	$160.10
Purchase #5	$129.51	5.635%	$136.8079	$136.81	$136.80	$136.80
Purchase #6	$223.39	11.216%	$248.4454	$248.45	$248.45	$248.40
Purchase #7	$65.87	9.604%	$72.1962	$72.20	$72.20	$72.20
7 purchase totals =	$1,160.80		$1,271.4512	$1,271.46	$1,271.45	$1,271.40