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	$102.81	6.136%	$109.1184	$109.12	$109.10	$109.10
Purchase #2	$31.75	11.262%	$35.3257	$35.33	$35.35	$35.30
Purchase #3	$185.27	8.357%	$200.753	$200.75	$200.75	$200.80
Purchase #4	$87.94	10.254%	$96.9574	$96.96	$96.95	$97.00
Purchase #5	$204.74	11.247%	$227.7671	$227.77	$227.75	$227.80
Purchase #6	$191.76	9.185%	$209.3732	$209.37	$209.35	$209.40
Purchase #7	$210.37	9.559%	$230.4793	$230.48	$230.50	$230.50
7 purchase totals =	$1,014.64		$1,109.7741	$1,109.78	$1,109.75	$1,109.90