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	$88.43	12.799%	$99.7482	$99.75	$99.75	$99.70
Purchase #2	$150.91	9.278%	$164.9114	$164.91	$164.90	$164.90
Purchase #3	$91.99	7.357%	$98.7577	$98.76	$98.75	$98.80
Purchase #4	$73.40	10.826%	$81.3463	$81.35	$81.35	$81.30
Purchase #5	$116.62	9.720%	$127.9555	$127.96	$127.95	$128.00
Purchase #6	$127.46	4.604%	$133.3283	$133.33	$133.35	$133.30
Purchase #7	$132.84	7.271%	$142.4988	$142.50	$142.50	$142.50
7 purchase totals =	$781.65		$848.5462	$848.56	$848.55	$848.50