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	$156.61	6.131%	$166.2118	$166.21	$166.20	$166.20
Purchase #2	$45.77	3.300%	$47.2804	$47.28	$47.30	$47.30
Purchase #3	$217.96	9.635%	$238.9604	$238.96	$238.95	$239.00
Purchase #4	$78.44	5.240%	$82.5503	$82.55	$82.55	$82.60
Purchase #5	$150.93	3.674%	$156.4752	$156.48	$156.50	$156.50
Purchase #6	$250.54	9.729%	$274.915	$274.92	$274.90	$274.90
Purchase #7	$100.72	4.549%	$105.3018	$105.30	$105.30	$105.30
7 purchase totals =	$1,000.97		$1,071.6949	$1,071.70	$1,071.70	$1,071.80