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	$14.37	4.506%	$15.0175	$15.02	$15.00	$15.00
Purchase #2	$240.40	13.225%	$272.1929	$272.19	$272.20	$272.20
Purchase #3	$170.67	10.226%	$188.1227	$188.12	$188.10	$188.10
Purchase #4	$93.46	7.534%	$100.5013	$100.50	$100.50	$100.50
Purchase #5	$170.80	10.788%	$189.2259	$189.23	$189.25	$189.20
Purchase #6	$30.66	3.834%	$31.8355	$31.84	$31.85	$31.80
Purchase #7	$40.25	12.831%	$45.4145	$45.41	$45.40	$45.40
7 purchase totals =	$760.61		$842.3103	$842.31	$842.30	$842.20