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	$78.34	8.612%	$85.0866	$85.09	$85.10	$85.10
Purchase #2	$177.44	5.699%	$187.5523	$187.55	$187.55	$187.60
Purchase #3	$145.63	10.235%	$160.5352	$160.54	$160.55	$160.50
Purchase #4	$241.83	3.740%	$250.8744	$250.87	$250.85	$250.90
Purchase #5	$88.58	5.471%	$93.4262	$93.43	$93.45	$93.40
Purchase #6	$76.83	7.696%	$82.7428	$82.74	$82.75	$82.70
Purchase #7	$36.72	4.326%	$38.3085	$38.31	$38.30	$38.30
7 purchase totals =	$845.37		$898.5260	$898.53	$898.55	$898.50