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	$134.66	12.552%	$151.5625	$151.56	$151.55	$151.60
Purchase #2	$76.26	12.308%	$85.6461	$85.65	$85.65	$85.60
Purchase #3	$98.88	13.365%	$112.0953	$112.10	$112.10	$112.10
Purchase #4	$241.47	13.339%	$273.6797	$273.68	$273.70	$273.70
Purchase #5	$205.89	11.465%	$229.4953	$229.50	$229.50	$229.50
Purchase #6	$148.25	4.830%	$155.4105	$155.41	$155.40	$155.40
Purchase #7	$121.81	7.514%	$130.9628	$130.96	$130.95	$131.00
7 purchase totals =	$1,027.22		$1,138.8522	$1,138.86	$1,138.85	$1,138.90