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	$148.48	13.264%	$168.1744	$168.17	$168.15	$168.20
Purchase #2	$157.76	13.464%	$179.0008	$179.00	$179.00	$179.00
Purchase #3	$49.78	13.730%	$56.6148	$56.61	$56.60	$56.60
Purchase #4	$5.63	12.530%	$6.3354	$6.34	$6.35	$6.30
Purchase #5	$154.90	3.388%	$160.148	$160.15	$160.15	$160.10
Purchase #6	$33.97	13.213%	$38.4585	$38.46	$38.45	$38.50
Purchase #7	$126.53	3.730%	$131.2496	$131.25	$131.25	$131.20
7 purchase totals =	$677.05		$739.9815	$739.98	$739.95	$739.90