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	$157.91	6.715%	$168.5137	$168.51	$168.50	$168.50
Purchase #2	$233.82	12.466%	$262.968	$262.97	$262.95	$263.00
Purchase #3	$150.45	13.498%	$170.7577	$170.76	$170.75	$170.80
Purchase #4	$136.40	4.688%	$142.7944	$142.79	$142.80	$142.80
Purchase #5	$97.39	7.630%	$104.8209	$104.82	$104.80	$104.80
Purchase #6	$167.98	7.471%	$180.5298	$180.53	$180.55	$180.50
Purchase #7	$184.88	4.661%	$193.4973	$193.50	$193.50	$193.50
7 purchase totals =	$1,128.83		$1,223.8818	$1,223.88	$1,223.85	$1,223.90