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	$7.30	12.606%	$8.2202	$8.22	$8.20	$8.20
Purchase #2	$57.52	6.686%	$61.3658	$61.37	$61.35	$61.40
Purchase #3	$185.56	8.688%	$201.6815	$201.68	$201.70	$201.70
Purchase #4	$160.31	12.675%	$180.6293	$180.63	$180.65	$180.60
Purchase #5	$192.56	11.726%	$215.1396	$215.14	$215.15	$215.10
Purchase #6	$238.61	10.667%	$264.0625	$264.06	$264.05	$264.10
Purchase #7	$233.36	13.514%	$264.8963	$264.90	$264.90	$264.90
7 purchase totals =	$1,075.22		$1,195.9952	$1,196.00	$1,196.00	$1,196.00