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	$121.69	12.284%	$136.6384	$136.64	$136.65	$136.60
Purchase #2	$236.31	12.527%	$265.9126	$265.91	$265.90	$265.90
Purchase #3	$142.63	3.463%	$147.5693	$147.57	$147.55	$147.60
Purchase #4	$48.66	3.171%	$50.203	$50.20	$50.20	$50.20
Purchase #5	$99.88	12.407%	$112.2721	$112.27	$112.25	$112.30
Purchase #6	$162.28	13.733%	$184.5659	$184.57	$184.55	$184.60
Purchase #7	$108.29	10.112%	$119.2403	$119.24	$119.25	$119.20
7 purchase totals =	$919.74		$1,016.4016	$1,016.40	$1,016.35	$1,016.40