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	$83.68	8.601%	$90.8773	$90.88	$90.90	$90.90
Purchase #2	$147.51	7.483%	$158.5482	$158.55	$158.55	$158.50
Purchase #3	$82.37	3.660%	$85.3847	$85.38	$85.40	$85.40
Purchase #4	$43.49	5.306%	$45.7976	$45.80	$45.80	$45.80
Purchase #5	$32.44	8.789%	$35.2912	$35.29	$35.30	$35.30
Purchase #6	$162.39	13.526%	$184.3549	$184.35	$184.35	$184.40
Purchase #7	$229.54	3.646%	$237.909	$237.91	$237.90	$237.90
7 purchase totals =	$781.42		$838.1629	$838.16	$838.20	$838.20