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	$35.30	7.500%	$37.9475	$37.95	$37.95	$37.90
Purchase #2	$170.60	8.622%	$185.3091	$185.31	$185.30	$185.30
Purchase #3	$249.88	6.501%	$266.1247	$266.12	$266.10	$266.10
Purchase #4	$151.60	11.252%	$168.658	$168.66	$168.65	$168.70
Purchase #5	$236.96	9.677%	$259.8906	$259.89	$259.90	$259.90
Purchase #6	$40.79	4.568%	$42.6533	$42.65	$42.65	$42.70
Purchase #7	$153.92	9.421%	$168.4208	$168.42	$168.40	$168.40
7 purchase totals =	$1,039.05		$1,129.0040	$1,129.00	$1,128.95	$1,129.00