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	$35.68	9.440%	$39.0482	$39.05	$39.05	$39.00
Purchase #2	$56.89	4.715%	$59.5724	$59.57	$59.55	$59.60
Purchase #3	$180.55	4.577%	$188.8138	$188.81	$188.80	$188.80
Purchase #4	$91.82	7.603%	$98.8011	$98.80	$98.80	$98.80
Purchase #5	$76.61	11.181%	$85.1758	$85.18	$85.20	$85.20
Purchase #6	$197.86	13.732%	$225.0301	$225.03	$225.05	$225.00
Purchase #7	$138.28	3.220%	$142.7326	$142.73	$142.75	$142.70
7 purchase totals =	$777.69		$839.1740	$839.17	$839.20	$839.10