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	$31.63	12.130%	$35.4667	$35.47	$35.45	$35.50
Purchase #2	$132.96	11.176%	$147.8196	$147.82	$147.80	$147.80
Purchase #3	$90.74	8.194%	$98.1752	$98.18	$98.20	$98.20
Purchase #4	$11.33	10.638%	$12.5353	$12.54	$12.55	$12.50
Purchase #5	$128.77	5.130%	$135.3759	$135.38	$135.40	$135.40
Purchase #6	$113.61	8.854%	$123.669	$123.67	$123.65	$123.70
Purchase #7	$82.49	3.118%	$85.062	$85.06	$85.05	$85.10
7 purchase totals =	$591.53		$638.1037	$638.12	$638.10	$638.20