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	$82.38	8.742%	$89.5817	$89.58	$89.60	$89.60
Purchase #2	$135.44	7.361%	$145.4097	$145.41	$145.40	$145.40
Purchase #3	$99.36	5.597%	$104.9212	$104.92	$104.90	$104.90
Purchase #4	$190.25	8.171%	$205.7953	$205.80	$205.80	$205.80
Purchase #5	$157.34	12.811%	$177.4968	$177.50	$177.50	$177.50
Purchase #6	$178.75	5.526%	$188.6277	$188.63	$188.65	$188.60
Purchase #7	$51.50	12.281%	$57.8247	$57.82	$57.80	$57.80
7 purchase totals =	$895.02		$969.6571	$969.66	$969.65	$969.60