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	$37.50	9.134%	$40.9253	$40.93	$40.95	$40.90
Purchase #2	$47.35	7.497%	$50.8998	$50.90	$50.90	$50.90
Purchase #3	$145.43	7.655%	$156.5627	$156.56	$156.55	$156.60
Purchase #4	$16.42	10.236%	$18.1008	$18.10	$18.10	$18.10
Purchase #5	$134.96	11.316%	$150.2321	$150.23	$150.25	$150.20
Purchase #6	$94.85	4.168%	$98.8033	$98.80	$98.80	$98.80
Purchase #7	$132.61	8.859%	$144.3579	$144.36	$144.35	$144.40
7 purchase totals =	$609.12		$659.8819	$659.88	$659.90	$659.90