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	$136.44	11.866%	$152.63	$152.63	$152.65	$152.60
Purchase #2	$160.73	8.359%	$174.1654	$174.17	$174.15	$174.20
Purchase #3	$128.61	8.175%	$139.1239	$139.12	$139.10	$139.10
Purchase #4	$186.81	11.830%	$208.9096	$208.91	$208.90	$208.90
Purchase #5	$50.53	4.652%	$52.8807	$52.88	$52.90	$52.90
Purchase #6	$41.79	10.186%	$46.0467	$46.05	$46.05	$46.00
Purchase #7	$81.37	11.410%	$90.6543	$90.65	$90.65	$90.70
7 purchase totals =	$786.28		$864.4106	$864.41	$864.40	$864.40