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	$137.40	13.402%	$155.8143	$155.81	$155.80	$155.80
Purchase #2	$210.97	13.211%	$238.8412	$238.84	$238.85	$238.80
Purchase #3	$86.50	6.873%	$92.4451	$92.45	$92.45	$92.40
Purchase #4	$179.52	11.746%	$200.6064	$200.61	$200.60	$200.60
Purchase #5	$29.35	6.351%	$31.214	$31.21	$31.20	$31.20
Purchase #6	$121.67	7.860%	$131.2333	$131.23	$131.25	$131.20
Purchase #7	$199.28	5.518%	$210.2763	$210.28	$210.30	$210.30
7 purchase totals =	$964.69		$1,060.4306	$1,060.43	$1,060.45	$1,060.30