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	$41.89	4.627%	$43.8283	$43.83	$43.85	$43.80
Purchase #2	$38.43	5.196%	$40.4268	$40.43	$40.45	$40.40
Purchase #3	$227.96	7.319%	$244.6444	$244.64	$244.65	$244.60
Purchase #4	$6.56	3.830%	$6.8112	$6.81	$6.80	$6.80
Purchase #5	$28.76	10.677%	$31.8307	$31.83	$31.85	$31.80
Purchase #6	$115.27	10.841%	$127.7664	$127.77	$127.75	$127.80
Purchase #7	$55.84	8.874%	$60.7952	$60.80	$60.80	$60.80
7 purchase totals =	$514.71		$556.1030	$556.11	$556.15	$556.00