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	$35.61	10.594%	$39.3825	$39.38	$39.40	$39.40
Purchase #2	$109.70	13.423%	$124.425	$124.43	$124.45	$124.40
Purchase #3	$68.64	5.459%	$72.3871	$72.39	$72.40	$72.40
Purchase #4	$205.94	6.764%	$219.8698	$219.87	$219.85	$219.90
Purchase #5	$144.40	12.199%	$162.0154	$162.02	$162.00	$162.00
Purchase #6	$55.81	5.630%	$58.9521	$58.95	$58.95	$59.00
Purchase #7	$47.63	9.767%	$52.282	$52.28	$52.30	$52.30
7 purchase totals =	$667.73		$729.3139	$729.32	$729.35	$729.40