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	$11.58	13.453%	$13.1379	$13.14	$13.15	$13.10
Purchase #2	$215.58	3.598%	$223.3366	$223.34	$223.35	$223.30
Purchase #3	$171.37	11.476%	$191.0364	$191.04	$191.05	$191.00
Purchase #4	$124.35	13.231%	$140.8027	$140.80	$140.80	$140.80
Purchase #5	$79.82	3.328%	$82.4764	$82.48	$82.50	$82.50
Purchase #6	$140.80	8.755%	$153.127	$153.13	$153.15	$153.10
Purchase #7	$241.31	3.847%	$250.5932	$250.59	$250.60	$250.60
7 purchase totals =	$984.81		$1,054.5102	$1,054.52	$1,054.60	$1,054.40