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	$29.64	7.174%	$31.7664	$31.77	$31.75	$31.80
Purchase #2	$245.59	11.243%	$273.2017	$273.20	$273.20	$273.20
Purchase #3	$130.53	8.113%	$141.1199	$141.12	$141.10	$141.10
Purchase #4	$98.82	12.379%	$111.0529	$111.05	$111.05	$111.10
Purchase #5	$93.75	9.346%	$102.5119	$102.51	$102.50	$102.50
Purchase #6	$198.38	11.848%	$221.8841	$221.88	$221.90	$221.90
Purchase #7	$187.29	6.529%	$199.5182	$199.52	$199.50	$199.50
7 purchase totals =	$984.00		$1,081.0551	$1,081.05	$1,081.00	$1,081.10