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	$35.43	6.256%	$37.6465	$37.65	$37.65	$37.60
Purchase #2	$88.92	12.360%	$99.9105	$99.91	$99.90	$99.90
Purchase #3	$128.27	7.463%	$137.8428	$137.84	$137.85	$137.80
Purchase #4	$58.67	10.616%	$64.8984	$64.90	$64.90	$64.90
Purchase #5	$192.91	6.685%	$205.806	$205.81	$205.80	$205.80
Purchase #6	$97.73	7.235%	$104.8008	$104.80	$104.80	$104.80
Purchase #7	$14.31	5.410%	$15.0842	$15.08	$15.10	$15.10
7 purchase totals =	$616.24		$665.9892	$665.99	$666.00	$665.90