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	$166.43	8.256%	$180.1705	$180.17	$180.15	$180.20
Purchase #2	$214.76	13.292%	$243.3059	$243.31	$243.30	$243.30
Purchase #3	$83.77	7.450%	$90.0109	$90.01	$90.00	$90.00
Purchase #4	$39.81	3.128%	$41.0553	$41.06	$41.05	$41.10
Purchase #5	$79.81	13.253%	$90.3872	$90.39	$90.40	$90.40
Purchase #6	$230.94	11.241%	$256.9	$256.90	$256.90	$256.90
Purchase #7	$84.87	12.360%	$95.3599	$95.36	$95.35	$95.40
7 purchase totals =	$900.39		$997.1897	$997.20	$997.15	$997.30