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	$249.39	7.648%	$268.4633	$268.46	$268.45	$268.50
Purchase #2	$196.55	7.738%	$211.759	$211.76	$211.75	$211.80
Purchase #3	$182.86	10.172%	$201.4605	$201.46	$201.45	$201.50
Purchase #4	$139.36	11.773%	$155.7669	$155.77	$155.75	$155.80
Purchase #5	$238.58	6.540%	$254.1831	$254.18	$254.20	$254.20
Purchase #6	$36.53	11.827%	$40.8504	$40.85	$40.85	$40.90
Purchase #7	$72.97	13.354%	$82.7144	$82.71	$82.70	$82.70
7 purchase totals =	$1,116.24		$1,215.1976	$1,215.19	$1,215.15	$1,215.40