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	$26.82	7.624%	$28.8648	$28.86	$28.85	$28.90
Purchase #2	$210.96	10.622%	$233.3682	$233.37	$233.35	$233.40
Purchase #3	$82.32	7.443%	$88.4471	$88.45	$88.45	$88.40
Purchase #4	$22.59	5.785%	$23.8968	$23.90	$23.90	$23.90
Purchase #5	$189.51	6.860%	$202.5104	$202.51	$202.50	$202.50
Purchase #6	$184.26	10.661%	$203.904	$203.90	$203.90	$203.90
Purchase #7	$213.71	4.179%	$222.6409	$222.64	$222.65	$222.60
7 purchase totals =	$930.17		$1,003.6322	$1,003.63	$1,003.60	$1,003.60