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	$204.99	10.674%	$226.8706	$226.87	$226.85	$226.90
Purchase #2	$72.71	12.422%	$81.742	$81.74	$81.75	$81.70
Purchase #3	$133.49	7.506%	$143.5098	$143.51	$143.50	$143.50
Purchase #4	$137.98	13.410%	$156.4831	$156.48	$156.50	$156.50
Purchase #5	$90.43	3.450%	$93.5498	$93.55	$93.55	$93.50
Purchase #6	$59.48	5.165%	$62.5521	$62.55	$62.55	$62.60
Purchase #7	$52.43	5.853%	$55.4987	$55.50	$55.50	$55.50
7 purchase totals =	$751.51		$820.2061	$820.20	$820.20	$820.20