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	$113.79	6.811%	$121.5402	$121.54	$121.55	$121.50
Purchase #2	$14.67	5.398%	$15.4619	$15.46	$15.45	$15.50
Purchase #3	$110.26	3.602%	$114.2316	$114.23	$114.25	$114.20
Purchase #4	$96.45	6.284%	$102.5109	$102.51	$102.50	$102.50
Purchase #5	$10.78	10.420%	$11.9033	$11.90	$11.90	$11.90
Purchase #6	$56.31	5.368%	$59.3327	$59.33	$59.35	$59.30
Purchase #7	$28.35	3.365%	$29.304	$29.30	$29.30	$29.30
7 purchase totals =	$430.61		$454.2846	$454.27	$454.30	$454.20