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	$164.82	13.542%	$187.1399	$187.14	$187.15	$187.10
Purchase #2	$103.98	7.189%	$111.4551	$111.46	$111.45	$111.50
Purchase #3	$94.50	3.480%	$97.7886	$97.79	$97.80	$97.80
Purchase #4	$222.87	10.621%	$246.541	$246.54	$246.55	$246.50
Purchase #5	$76.85	9.442%	$84.1062	$84.11	$84.10	$84.10
Purchase #6	$83.56	3.407%	$86.4069	$86.41	$86.40	$86.40
Purchase #7	$90.67	9.699%	$99.4641	$99.46	$99.45	$99.50
7 purchase totals =	$837.25		$912.9018	$912.91	$912.90	$912.90