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	$93.39	6.293%	$99.267	$99.27	$99.25	$99.30
Purchase #2	$78.63	10.237%	$86.6794	$86.68	$86.70	$86.70
Purchase #3	$124.53	12.871%	$140.5583	$140.56	$140.55	$140.60
Purchase #4	$51.85	9.590%	$56.8224	$56.82	$56.80	$56.80
Purchase #5	$200.25	9.447%	$219.1676	$219.17	$219.15	$219.20
Purchase #6	$155.70	7.232%	$166.9602	$166.96	$166.95	$167.00
Purchase #7	$186.68	7.288%	$200.2852	$200.29	$200.30	$200.30
7 purchase totals =	$891.03		$969.7401	$969.75	$969.70	$969.90