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	$230.65	4.869%	$241.8803	$241.88	$241.90	$241.90
Purchase #2	$156.86	7.253%	$168.2371	$168.24	$168.25	$168.20
Purchase #3	$158.57	8.540%	$172.1119	$172.11	$172.10	$172.10
Purchase #4	$195.91	11.679%	$218.7903	$218.79	$218.80	$218.80
Purchase #5	$5.28	10.185%	$5.8178	$5.82	$5.80	$5.80
Purchase #6	$242.59	11.249%	$269.8789	$269.88	$269.90	$269.90
Purchase #7	$131.52	4.274%	$137.1412	$137.14	$137.15	$137.10
7 purchase totals =	$1,121.38		$1,213.8575	$1,213.86	$1,213.90	$1,213.80