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	$79.47	12.302%	$89.2464	$89.25	$89.25	$89.20
Purchase #2	$105.56	7.222%	$113.1835	$113.18	$113.20	$113.20
Purchase #3	$12.78	8.230%	$13.8318	$13.83	$13.85	$13.80
Purchase #4	$203.45	11.334%	$226.509	$226.51	$226.50	$226.50
Purchase #5	$245.64	12.586%	$276.5563	$276.56	$276.55	$276.60
Purchase #6	$103.89	12.792%	$117.1796	$117.18	$117.20	$117.20
Purchase #7	$146.89	5.799%	$155.4082	$155.41	$155.40	$155.40
7 purchase totals =	$897.68		$991.9148	$991.92	$991.95	$991.90