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	$58.71	9.665%	$64.3843	$64.38	$64.40	$64.40
Purchase #2	$82.34	7.710%	$88.6884	$88.69	$88.70	$88.70
Purchase #3	$196.75	12.364%	$221.0762	$221.08	$221.10	$221.10
Purchase #4	$16.81	8.655%	$18.2649	$18.26	$18.25	$18.30
Purchase #5	$176.25	7.387%	$189.2696	$189.27	$189.25	$189.30
Purchase #6	$164.26	5.261%	$172.9017	$172.90	$172.90	$172.90
Purchase #7	$150.49	12.223%	$168.8844	$168.88	$168.90	$168.90
7 purchase totals =	$845.61		$923.4695	$923.46	$923.50	$923.60