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	$147.38	12.816%	$166.2682	$166.27	$166.25	$166.30
Purchase #2	$66.30	10.315%	$73.1388	$73.14	$73.15	$73.10
Purchase #3	$234.27	10.345%	$258.5052	$258.51	$258.50	$258.50
Purchase #4	$212.94	12.462%	$239.4766	$239.48	$239.50	$239.50
Purchase #5	$180.41	10.209%	$198.8281	$198.83	$198.85	$198.80
Purchase #6	$67.41	6.126%	$71.5395	$71.54	$71.55	$71.50
Purchase #7	$164.62	7.667%	$177.2414	$177.24	$177.25	$177.20
7 purchase totals =	$1,073.33		$1,184.9978	$1,185.01	$1,185.05	$1,184.90