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	$70.47	10.649%	$77.9744	$77.97	$77.95	$78.00
Purchase #2	$185.83	13.726%	$211.337	$211.34	$211.35	$211.30
Purchase #3	$82.59	11.701%	$92.2539	$92.25	$92.25	$92.30
Purchase #4	$239.56	12.754%	$270.1135	$270.11	$270.10	$270.10
Purchase #5	$168.50	9.462%	$184.4435	$184.44	$184.45	$184.40
Purchase #6	$210.60	8.413%	$228.3178	$228.32	$228.30	$228.30
Purchase #7	$217.82	12.230%	$244.4594	$244.46	$244.45	$244.50
7 purchase totals =	$1,175.37		$1,308.8995	$1,308.89	$1,308.85	$1,308.90