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	$104.89	10.796%	$116.2139	$116.21	$116.20	$116.20
Purchase #2	$82.93	13.503%	$94.128	$94.13	$94.15	$94.10
Purchase #3	$97.50	3.825%	$101.2294	$101.23	$101.25	$101.20
Purchase #4	$5.46	12.225%	$6.1275	$6.13	$6.15	$6.10
Purchase #5	$66.26	6.518%	$70.5788	$70.58	$70.60	$70.60
Purchase #6	$40.78	4.359%	$42.5576	$42.56	$42.55	$42.60
Purchase #7	$219.48	8.577%	$238.3048	$238.30	$238.30	$238.30
7 purchase totals =	$617.30		$669.1400	$669.14	$669.20	$669.10