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	$91.61	12.201%	$102.7873	$102.79	$102.80	$102.80
Purchase #2	$33.81	10.181%	$37.2522	$37.25	$37.25	$37.30
Purchase #3	$157.76	13.442%	$178.9661	$178.97	$178.95	$179.00
Purchase #4	$245.51	4.752%	$257.1766	$257.18	$257.20	$257.20
Purchase #5	$92.82	10.842%	$102.8835	$102.88	$102.90	$102.90
Purchase #6	$19.53	4.842%	$20.4756	$20.48	$20.50	$20.50
Purchase #7	$40.74	5.347%	$42.9184	$42.92	$42.90	$42.90
7 purchase totals =	$681.78		$742.4597	$742.47	$742.50	$742.60