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	$49.98	12.737%	$56.346	$56.35	$56.35	$56.30
Purchase #2	$184.53	10.300%	$203.5366	$203.54	$203.55	$203.50
Purchase #3	$174.80	11.214%	$194.4021	$194.40	$194.40	$194.40
Purchase #4	$165.75	3.259%	$171.1518	$171.15	$171.15	$171.20
Purchase #5	$225.89	5.761%	$238.9035	$238.90	$238.90	$238.90
Purchase #6	$80.61	11.456%	$89.8447	$89.84	$89.85	$89.80
Purchase #7	$163.42	13.282%	$185.1254	$185.13	$185.15	$185.10
7 purchase totals =	$1,044.98		$1,139.3101	$1,139.31	$1,139.35	$1,139.20