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	$180.69	3.710%	$187.3936	$187.39	$187.40	$187.40
Purchase #2	$97.45	13.129%	$110.2442	$110.24	$110.25	$110.20
Purchase #3	$129.89	13.836%	$147.8616	$147.86	$147.85	$147.90
Purchase #4	$123.81	7.650%	$133.2815	$133.28	$133.30	$133.30
Purchase #5	$134.55	6.856%	$143.7747	$143.77	$143.75	$143.80
Purchase #6	$105.63	3.686%	$109.5235	$109.52	$109.50	$109.50
Purchase #7	$37.30	6.829%	$39.8472	$39.85	$39.85	$39.80
7 purchase totals =	$809.32		$871.9263	$871.91	$871.90	$871.90