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	$160.42	7.507%	$172.4627	$172.46	$172.45	$172.50
Purchase #2	$230.90	10.840%	$255.9296	$255.93	$255.95	$255.90
Purchase #3	$61.35	8.265%	$66.4206	$66.42	$66.40	$66.40
Purchase #4	$20.78	3.360%	$21.4782	$21.48	$21.50	$21.50
Purchase #5	$148.47	3.473%	$153.6264	$153.63	$153.65	$153.60
Purchase #6	$135.69	8.377%	$147.0568	$147.06	$147.05	$147.10
Purchase #7	$35.52	12.715%	$40.0364	$40.04	$40.05	$40.00
7 purchase totals =	$793.13		$857.0107	$857.02	$857.05	$857.00