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	$229.83	12.666%	$258.9403	$258.94	$258.95	$258.90
Purchase #2	$26.61	6.730%	$28.4009	$28.40	$28.40	$28.40
Purchase #3	$187.93	6.604%	$200.3409	$200.34	$200.35	$200.30
Purchase #4	$225.89	9.741%	$247.8939	$247.89	$247.90	$247.90
Purchase #5	$40.39	6.441%	$42.9915	$42.99	$43.00	$43.00
Purchase #6	$77.97	9.495%	$85.3733	$85.37	$85.35	$85.40
Purchase #7	$108.72	10.638%	$120.2856	$120.29	$120.30	$120.30
7 purchase totals =	$897.34		$984.2264	$984.22	$984.25	$984.20