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	$121.81	12.611%	$137.1715	$137.17	$137.15	$137.20
Purchase #2	$184.93	10.773%	$204.8525	$204.85	$204.85	$204.90
Purchase #3	$209.92	6.633%	$223.844	$223.84	$223.85	$223.80
Purchase #4	$49.90	7.288%	$53.5367	$53.54	$53.55	$53.50
Purchase #5	$119.98	9.445%	$131.3121	$131.31	$131.30	$131.30
Purchase #6	$38.82	13.473%	$44.0502	$44.05	$44.05	$44.10
Purchase #7	$24.82	10.787%	$27.4973	$27.50	$27.50	$27.50
7 purchase totals =	$750.18		$822.2643	$822.26	$822.25	$822.30