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	$37.37	4.790%	$39.16	$39.16	$39.15	$39.20
Purchase #2	$87.32	13.244%	$98.8847	$98.88	$98.90	$98.90
Purchase #3	$54.48	8.870%	$59.3124	$59.31	$59.30	$59.30
Purchase #4	$223.46	11.833%	$249.902	$249.90	$249.90	$249.90
Purchase #5	$86.42	13.594%	$98.1679	$98.17	$98.15	$98.20
Purchase #6	$94.79	13.623%	$107.7032	$107.70	$107.70	$107.70
Purchase #7	$196.91	9.873%	$216.3509	$216.35	$216.35	$216.40
7 purchase totals =	$780.75		$869.4811	$869.47	$869.45	$869.60