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	$11.89	12.103%	$13.329	$13.33	$13.35	$13.30
Purchase #2	$136.35	7.363%	$146.3895	$146.39	$146.40	$146.40
Purchase #3	$40.31	12.811%	$45.4741	$45.47	$45.45	$45.50
Purchase #4	$143.41	9.294%	$156.7385	$156.74	$156.75	$156.70
Purchase #5	$168.77	5.722%	$178.427	$178.43	$178.45	$178.40
Purchase #6	$203.98	8.348%	$221.0083	$221.01	$221.00	$221.00
Purchase #7	$115.87	6.612%	$123.5313	$123.53	$123.55	$123.50
7 purchase totals =	$820.58		$884.8977	$884.90	$884.95	$884.80