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	$35.53	6.541%	$37.854	$37.85	$37.85	$37.90
Purchase #2	$111.73	4.474%	$116.7288	$116.73	$116.75	$116.70
Purchase #3	$117.56	12.569%	$132.3361	$132.34	$132.35	$132.30
Purchase #4	$145.62	3.408%	$150.5827	$150.58	$150.60	$150.60
Purchase #5	$97.51	12.701%	$109.8947	$109.89	$109.90	$109.90
Purchase #6	$250.61	5.493%	$264.376	$264.38	$264.40	$264.40
Purchase #7	$230.76	11.339%	$256.9259	$256.93	$256.95	$256.90
7 purchase totals =	$989.32		$1,068.6982	$1,068.70	$1,068.80	$1,068.70