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	$38.66	8.322%	$41.8773	$41.88	$41.90	$41.90
Purchase #2	$85.85	5.243%	$90.3511	$90.35	$90.35	$90.40
Purchase #3	$57.91	5.392%	$61.0325	$61.03	$61.05	$61.00
Purchase #4	$21.59	13.749%	$24.5584	$24.56	$24.55	$24.60
Purchase #5	$146.72	12.209%	$164.633	$164.63	$164.65	$164.60
Purchase #6	$219.47	12.309%	$246.4846	$246.48	$246.50	$246.50
Purchase #7	$28.31	6.637%	$30.1889	$30.19	$30.20	$30.20
7 purchase totals =	$598.51		$659.1258	$659.12	$659.20	$659.20