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	$156.55	5.735%	$165.5281	$165.53	$165.55	$165.50
Purchase #2	$49.91	12.681%	$56.2391	$56.24	$56.25	$56.20
Purchase #3	$202.70	9.751%	$222.4653	$222.47	$222.45	$222.50
Purchase #4	$84.97	9.189%	$92.7779	$92.78	$92.80	$92.80
Purchase #5	$250.35	9.829%	$274.9569	$274.96	$274.95	$275.00
Purchase #6	$86.73	9.402%	$94.8844	$94.88	$94.90	$94.90
Purchase #7	$102.63	8.748%	$111.6081	$111.61	$111.60	$111.60
7 purchase totals =	$933.84		$1,018.4598	$1,018.47	$1,018.50	$1,018.50