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	$43.31	13.580%	$49.1915	$49.19	$49.20	$49.20
Purchase #2	$154.90	9.291%	$169.2918	$169.29	$169.30	$169.30
Purchase #3	$83.55	11.109%	$92.8316	$92.83	$92.85	$92.80
Purchase #4	$35.51	6.646%	$37.87	$37.87	$37.85	$37.90
Purchase #5	$50.74	8.691%	$55.1498	$55.15	$55.15	$55.10
Purchase #6	$132.59	8.853%	$144.3282	$144.33	$144.35	$144.30
Purchase #7	$219.90	11.523%	$245.2391	$245.24	$245.25	$245.20
7 purchase totals =	$720.50		$793.9020	$793.90	$793.95	$793.80