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	$89.81	13.142%	$101.6128	$101.61	$101.60	$101.60
Purchase #2	$126.96	11.290%	$141.2938	$141.29	$141.30	$141.30
Purchase #3	$142.53	10.691%	$157.7679	$157.77	$157.75	$157.80
Purchase #4	$223.75	9.180%	$244.2903	$244.29	$244.30	$244.30
Purchase #5	$211.25	6.336%	$224.6348	$224.63	$224.65	$224.60
Purchase #6	$28.50	11.837%	$31.8735	$31.87	$31.85	$31.90
Purchase #7	$107.36	9.741%	$117.8179	$117.82	$117.80	$117.80
7 purchase totals =	$930.16		$1,019.2910	$1,019.28	$1,019.25	$1,019.30