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	$133.41	9.360%	$145.8972	$145.90	$145.90	$145.90
Purchase #2	$38.58	12.698%	$43.4789	$43.48	$43.50	$43.50
Purchase #3	$33.62	11.416%	$37.4581	$37.46	$37.45	$37.50
Purchase #4	$63.36	13.174%	$71.707	$71.71	$71.70	$71.70
Purchase #5	$96.60	10.165%	$106.4194	$106.42	$106.40	$106.40
Purchase #6	$71.52	9.797%	$78.5268	$78.53	$78.55	$78.50
Purchase #7	$126.54	8.810%	$137.6882	$137.69	$137.70	$137.70
7 purchase totals =	$563.63		$621.1756	$621.19	$621.20	$621.20