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	$122.93	13.764%	$139.8501	$139.85	$139.85	$139.90
Purchase #2	$39.79	13.702%	$45.242	$45.24	$45.25	$45.20
Purchase #3	$206.95	11.377%	$230.4947	$230.49	$230.50	$230.50
Purchase #4	$200.75	4.775%	$210.3358	$210.34	$210.35	$210.30
Purchase #5	$187.30	3.730%	$194.2863	$194.29	$194.30	$194.30
Purchase #6	$27.75	6.540%	$29.5649	$29.56	$29.55	$29.60
Purchase #7	$83.75	6.730%	$89.3864	$89.39	$89.40	$89.40
7 purchase totals =	$869.22		$939.1602	$939.16	$939.20	$939.20