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	$80.34	11.538%	$89.6096	$89.61	$89.60	$89.60
Purchase #2	$125.92	12.440%	$141.5844	$141.58	$141.60	$141.60
Purchase #3	$105.95	3.228%	$109.3701	$109.37	$109.35	$109.40
Purchase #4	$27.26	7.592%	$29.3296	$29.33	$29.35	$29.30
Purchase #5	$144.35	11.214%	$160.5374	$160.54	$160.55	$160.50
Purchase #6	$32.29	8.799%	$35.1312	$35.13	$35.15	$35.10
Purchase #7	$158.91	11.873%	$177.7774	$177.78	$177.80	$177.80
7 purchase totals =	$675.02		$743.3397	$743.34	$743.40	$743.30