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	$95.78	8.412%	$103.837	$103.84	$103.85	$103.80
Purchase #2	$150.55	11.502%	$167.8663	$167.87	$167.85	$167.90
Purchase #3	$230.50	6.174%	$244.7311	$244.73	$244.75	$244.70
Purchase #4	$78.43	5.713%	$82.9107	$82.91	$82.90	$82.90
Purchase #5	$64.93	10.219%	$71.5652	$71.57	$71.55	$71.60
Purchase #6	$30.59	10.788%	$33.89	$33.89	$33.90	$33.90
Purchase #7	$180.25	3.515%	$186.5858	$186.59	$186.60	$186.60
7 purchase totals =	$831.03		$891.3861	$891.40	$891.40	$891.40