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	$109.32	11.245%	$121.613	$121.61	$121.60	$121.60
Purchase #2	$61.58	5.758%	$65.1258	$65.13	$65.15	$65.10
Purchase #3	$126.55	3.802%	$131.3614	$131.36	$131.35	$131.40
Purchase #4	$158.32	8.216%	$171.3276	$171.33	$171.35	$171.30
Purchase #5	$5.39	8.160%	$5.8298	$5.83	$5.85	$5.80
Purchase #6	$133.56	7.800%	$143.9777	$143.98	$144.00	$144.00
Purchase #7	$145.80	3.303%	$150.6158	$150.62	$150.60	$150.60
7 purchase totals =	$740.52		$789.8511	$789.86	$789.90	$789.80