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	$109.67	10.740%	$121.4486	$121.45	$121.45	$121.40
Purchase #2	$178.78	7.572%	$192.3172	$192.32	$192.30	$192.30
Purchase #3	$14.35	11.416%	$15.9882	$15.99	$16.00	$16.00
Purchase #4	$88.94	11.680%	$99.3282	$99.33	$99.35	$99.30
Purchase #5	$180.49	11.127%	$200.5731	$200.57	$200.55	$200.60
Purchase #6	$27.67	13.819%	$31.4937	$31.49	$31.50	$31.50
Purchase #7	$114.87	11.753%	$128.3707	$128.37	$128.35	$128.40
7 purchase totals =	$714.77		$789.5197	$789.52	$789.50	$789.50